Jak stworzyć kolekcję wielopoziomową?

using System;
using System.Collections.Generic;
using System.Windows;
using System.Collections.ObjectModel;

namespace WpfTutorialSamples.TreeView_control
{
        public partial class TreeViewMultipleTemplatesSample : Window
        {
                public TreeViewMultipleTemplatesSample()
                {
                        InitializeComponent();

                        List<Family> families = new List<Family>();

                        Family family1 = new Family() { Name = "The Doe's" };
                        family1.Members.Add(new FamilyMember() { Name = "John Doe", Age = 42 });
                        family1.Members.Add(new FamilyMember() { Name = "Jane Doe", Age = 39 });
                        family1.Members.Add(new FamilyMember() { Name = "Sammy Doe", Age = 13 });
                        families.Add(family1);

                        Family family2 = new Family() { Name = "The Moe's" };
                        family2.Members.Add(new FamilyMember() { Name = "Mark Moe", Age = 31 });
                        family2.Members.Add(new FamilyMember() { Name = "Norma Moe", Age = 28 });
                        families.Add(family2);

                        trvFamilies.ItemsSource = families;
                }
        }

        public class Family
        {
                public Family()
                {
                        this.Members = new ObservableCollection<FamilyMember>();
                }

                public string Name { get; set; }

                public ObservableCollection<FamilyMember> Members { get; set; }
        }

        public class FamilyMember
        {
                public string Name { get; set; }

                public int Age { get; set; }
        }
}

        public class FamilyMember
        {
                public FamilyMember()
                {
                        this.Children= new ObservableCollection<FamilyMember>();
                }
 
                public string Name { get; set; }
                public int Age { get; set; }
 
                public ObservableCollection<FamilyMember> Children { get; set; }
        }
 

List<FamilyMember> families = new List<FamilyMember>();

FamilyMember family1 = new FamilyMember() { Name = "The Doe's" };
family1.Children.Add(new FamilyMember() { Name = "John Doe", Age = 42 });
family1.Children.Add(new FamilyMember() { Name = "Jane Doe", Age = 39 });
family1.Children.Add(new FamilyMember() { Name = "Sammy Doe", Age = 13 });
families.Add(family1);

FamilyMember family2 = new FamilyMember() { Name = "The Moe's" };
family2.Children.Add(new FamilyMember() { Name = "Mark Moe", Age = 31 });
family2.Children.Add(new FamilyMember() { Name = "Norma Moe", Age = 28 });
families.Add(family2);
// i tu istotna czesc
FamilyMember level1 = new FamilyMember() { Name = "family with grandchildren" };
FamilyMember level2 = new FamilyMember() { Name = "family with children" };
FamilyMember level3 = new FamilyMember() { Name = "child" };
level2.Children.Add(level3);
level1.Children.Add(level2);
families.Add(level1);

trvFamilies.ItemsSource = families;

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
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 System.Collections.ObjectModel;
using System.Data.Sql;
using System.Data.SqlClient;
using System.Data.SqlTypes;


namespace korektor_WPF.Pages
{
    public partial class ListaSrodkow : UserControl
    {
        public ListaSrodkow()
                {
                       
                        List<FamilyMember> families = new List<FamilyMember>();
                        FamilyMember family1 = new FamilyMember() { Name = "The Doe's" };
                        family1.Children.Add(new FamilyMember() { Name = "John Doe", Age = 42 });
                        family1.Children.Add(new FamilyMember() { Name = "Jane Doe", Age = 39 });
                        family1.Children.Add(new FamilyMember() { Name = "Sammy Doe", Age = 13 });
                        families.Add(family1);
                        FamilyMember family2 = new FamilyMember() { Name = "The Moe's" };
                        family2.Children.Add(new FamilyMember() { Name = "Mark Moe", Age = 31 });
                        family2.Children.Add(new FamilyMember() { Name = "Norma Moe", Age = 28 });
                        families.Add(family2);
                        // i tu istotna czesc
                        FamilyMember level1 = new FamilyMember() { Name = "family with grandchildren" };
                        FamilyMember level2 = new FamilyMember() { Name = "family with children" };
                        FamilyMember level3 = new FamilyMember() { Name = "child" };
                        level2.Children.Add(level3);
                        level1.Children.Add(level2);
                        families.Add(level1);
                        trvFamilies.ItemsSource = families;
                }
    }
    public class Family
    {
        public Family()
        {
            this.Members = new ObservableCollection<FamilyMember>();
        }

        public string Name { get; set; }

        public ObservableCollection<FamilyMember> Members { get; set; }
    }

    public class FamilyMember
    {
        public FamilyMember()
        {
            this.Children = new ObservableCollection<FamilyMember>();
        }
        public string Name { get; set; }
        public int Age { get; set; }

        public ObservableCollection<FamilyMember> Children { get; set; }
    }
}

<UserControl x:Class="korektor_WPF.Pages.ListaSrodkow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                xmlns:self="clr-namespace:korektor_WPF.Pages"
        xmlns:WindowTitle="ListaSrodkow" Height="1250" Width="1200">
    <Grid Margin="10">
        <TreeView Name="trvFamilies">
            <TreeView.Resources>
                <HierarchicalDataTemplate DataType="{x:Type self:Family}" ItemsSource="{Binding Members}">
                    <StackPanel Orientation="Horizontal">
                        <TextBlock Text="{Binding Name}" />
                        <TextBlock Text=" [" Foreground="Blue" />
                        <TextBlock Text="{Binding Members.Count}" Foreground="Blue" />
                        <TextBlock Text="]" Foreground="Blue" />
                    </StackPanel>
                </HierarchicalDataTemplate>
                <DataTemplate DataType="{x:Type self:FamilyMember}">
                    <StackPanel Orientation="Horizontal">
                        <TextBlock Text="{Binding Name}" />
                        <TextBlock Text=" (" Foreground="Green" />
                        <TextBlock Text="{Binding Age}" Foreground="Green" />
                        <TextBlock Text=" years)" Foreground="Green" />
                    </StackPanel>
                </DataTemplate>
            </TreeView.Resources>
        </TreeView>
    </Grid>
</UserControl>

<HierarchicalDataTemplate DataType="{x:Type self:Family}" ItemsSource="{Binding Members}">

<HierarchicalDataTemplate DataType="{x:Type self:FamilyMember}" ItemsSource="{Binding Children}">