<DataTemplate DataType="{x:Type local:Book}"
                x:Key="BookRowDataTemplate">
      <Border BorderBrush="Gray"
              BorderThickness="2"
              Margin="5">
          <Grid Margin="5">
              <Grid.Resources>
                  <Style TargetType="TextBlock" BasedOn="{StaticResource TbkStyle}"/>
              </Grid.Resources>
              <Grid.RowDefinitions>
                  <RowDefinition/>
                  <RowDefinition/>
                  <RowDefinition/>
              </Grid.RowDefinitions>
              <Grid.ColumnDefinitions>
                  <ColumnDefinition/>
                  <ColumnDefinition/>
                  <ColumnDefinition/>
              </Grid.ColumnDefinitions>
              <TextBlock Text="{Binding Id}" Grid.Row="0" Grid.Column="0"/>
              <TextBlock Text="{Binding Name}" Grid.Row="0" Grid.Column="1"/>
              <TextBlock Text="{Binding Comment}" Grid.Row="0" Grid.Column="2"/>
              <TextBlock Text="{Binding Content}" Grid.Row="1" Grid.Column="0"/>
              <TextBlock Text="{Binding ISBN}" Grid.Row="1" Grid.Column="1"/>
              <TextBlock Text="{Binding Summary}" Grid.Row="1" Grid.Column="2"/>
              <TextBlock Text="{Binding Author}" Grid.Row="2" Grid.Column="0"/>
              <TextBlock Text="{Binding Title}" Grid.Row="2" Grid.Column="1"/>
              <TextBlock Text="{Binding Topic}" Grid.Row="2" Grid.Column="2"/>
          </Grid>
      </Border>
  </DataTemplate>

  <HierarchicalDataTemplate DataType="{x:Type local:GroupedBook}"
                            ItemsSource="{Binding BksList}"
                            ItemTemplate="{StaticResource BookRowDataTemplate}"
                            x:Key="TreeViewItemTemplate">
      <GroupBox Header="{Binding GroupName}"
                FontSize="80"
                Margin="10,10,10,150"
                BorderBrush="Blue"
                BorderThickness="5"/>
  </HierarchicalDataTemplate>

<Window x:Class="WpfApp4.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp4"
        mc:Ignorable="d"
        Title="{Binding MainTitle}" WindowState="Maximized">
    <Window.DataContext>
        <local:MainVM/>
    </Window.DataContext>
    <Window.Resources>
        <Style TargetType="TextBlock" x:Key="TbkStyle">
            <Setter Property="FontSize" Value="30"/>
            <Style.Triggers>
                <Trigger Property="IsMouseOver" Value="True">
                    <Setter Property="Foreground" Value="Red"/>
                    <Setter Property="FontWeight" Value="ExtraBold"/>
                </Trigger>
            </Style.Triggers>
        </Style>

        <DataTemplate DataType="{x:Type local:Book}"
                      x:Key="BookRowDataTemplate">
            <Border BorderBrush="Gray"
                    BorderThickness="2"
                    Margin="5">
                <Grid Margin="5">
                    <Grid.Resources>
                        <Style TargetType="TextBlock" BasedOn="{StaticResource TbkStyle}"/>
                    </Grid.Resources>
                    <Grid.RowDefinitions>
                        <RowDefinition/>
                        <RowDefinition/>
                        <RowDefinition/>
                    </Grid.RowDefinitions>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition/>
                        <ColumnDefinition/>
                        <ColumnDefinition/>
                    </Grid.ColumnDefinitions>
                    <TextBlock Text="{Binding Id}" Grid.Row="0" Grid.Column="0"/>
                    <TextBlock Text="{Binding Name}" Grid.Row="0" Grid.Column="1"/>
                    <TextBlock Text="{Binding Comment}" Grid.Row="0" Grid.Column="2"/>
                    <TextBlock Text="{Binding Content}" Grid.Row="1" Grid.Column="0"/>
                    <TextBlock Text="{Binding ISBN}" Grid.Row="1" Grid.Column="1"/>
                    <TextBlock Text="{Binding Summary}" Grid.Row="1" Grid.Column="2"/>
                    <TextBlock Text="{Binding Author}" Grid.Row="2" Grid.Column="0"/>
                    <TextBlock Text="{Binding Title}" Grid.Row="2" Grid.Column="1"/>
                    <TextBlock Text="{Binding Topic}" Grid.Row="2" Grid.Column="2"/>
                </Grid>
            </Border>
        </DataTemplate>

        <HierarchicalDataTemplate DataType="{x:Type local:GroupedBook}"
                                  ItemsSource="{Binding BksList}"
                                  ItemTemplate="{StaticResource BookRowDataTemplate}"
                                  x:Key="TreeViewItemTemplate">
            <GroupBox Header="{Binding GroupName}"
                      FontSize="80"
                      Margin="10,10,10,150"
                      BorderBrush="Blue"
                      BorderThickness="5"/>
        </HierarchicalDataTemplate>

        <Style TargetType="TreeViewItem">
            <Setter Property="IsExpanded" Value="False"/>
        </Style>
    </Window.Resources>
    <Grid>
        <TreeView ItemsSource="{Binding GroupedBksCollection}"
                  ItemTemplate="{StaticResource TreeViewItemTemplate}"/>
    </Grid>
</Window>




using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Net;
using System.Net.Http;
using System.Runtime.CompilerServices;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using Newtonsoft.Json;

namespace WpfApp4
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
    }

    public class MainVM : INotifyPropertyChanged
    {
        private static HttpClient httpClient = new HttpClient()
        {
            Timeout = TimeSpan.FromHours(1)
        };

        string url = "http://localhost:5000/api/book/getbooks/";
        private bool isLoading = false;

        public MainVM()
        {
            if (!DesignerProperties.GetIsInDesignMode(new DependencyObject()))
            {
                _ = InitBooksAsync(10);
            }
        }

        private async Task InitBooksAsync(int cnt = 1000)
        {
            if (isLoading)
            {
                return;
            }
            isLoading = true;

            MainTitle = $"{DateTime.Now},loading...";
            try
            {
                string jsonStr = await httpClient.GetStringAsync($"{url}{cnt}");
                var bks = JsonConvert.DeserializeObject<List<Book>>(jsonStr);
                if (bks != null && bks.Any())
                {
                    var tempGroupedBks = bks.GroupBy(x => x.CategoryName);
                    if (tempGroupedBks != null && tempGroupedBks.Any())
                    {
                        GroupedBksCollection = new ObservableCollection<GroupedBook>();
                        foreach (var g in tempGroupedBks)
                        {
                            GroupedBksCollection.Add(new GroupedBook()
                            {
                                GroupName = g.Key,
                                BksList = g.ToList()
                            });
                        }
                    }
                    MainTitle = $"{DateTime.Now},loaded {bks.Count} items" +
                        $"FirstId:{bks.FirstOrDefault()?.Id}" +
                        $"LastId:{bks.LastOrDefault()?.Id}";
                    System.Diagnostics.Debug.WriteLine(MainTitle);
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex?.Message);
            }
            finally
            {
                isLoading = false;
            }
        }

        private string mainTitle = $"{DateTime.Now}";
        public string MainTitle
        {
            get
            {
                return mainTitle;
            }
            set
            {
                if (value != mainTitle)
                {
                    mainTitle = value;
                    OnPropertyChanged();
                }
            }
        }

        private ObservableCollection<GroupedBook> groupedBksCollection;
        public ObservableCollection<GroupedBook> GroupedBksCollection
        {
            get
            {
                return groupedBksCollection;
            }
            set
            {
                if (value != groupedBksCollection)
                {
                    groupedBksCollection = value;
                    OnPropertyChanged();
                }
            }
        }

        public event PropertyChangedEventHandler? PropertyChanged;
        private void OnPropertyChanged([CallerMemberName] string propName = "")
        {
            var handler = Volatile.Read(ref this.PropertyChanged);
            if (handler == null)
            {
                return;
            }
            handler(this, new PropertyChangedEventArgs(propName));
        }
    }

    public class GroupedBook
    {
        public string GroupName { get; set; }
        public List<Book> BksList { get; set; }
    }

    public class Book
    {
        public long Id { get; set; }
        public string Name { get; set; }
        public string Author { get; set; }
        public string CategoryName { get; set; }
        public string Comment { get; set; }
        public string Content { get; set; }
        public string ISBN { get; set; }
        public string Summary { get; set; }
        public string Title { get; set; }
        public string Topic { get; set; }
    }
}