Example for WPF Treeview data binding

I'm beginner for C# and WPF.

When I tried to figure out how to bind data to treeview, I find a example in Microsoft learn, the link is https://learn.microsoft.com/en-us/dotnet/api/system.windows.hierarchicaldatatemplate?view=windowsdesktop-7.0.

It is a pity in this example only XAML code is provided, for objects there is only description but not code. Please see the picture below for the objects description.

https://i.stack.imgur.com/1UMdX.jpg

I code the objects with my limited C# knowledge, as below.

Objects: ListLeagueList

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Collections.ObjectModel;

namespace Treeview01
{
    public class ListLeagueList : ObservableCollection<League>
    {
        public ListLeagueList() : base()
        {
            Add(new League("League A"));
            Add(new League("League B"));
            Add(new League("League C"));
        }
    }
}

Objects: League

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Collections.ObjectModel;

namespace Treeview01
{
    public class League
    {
        public string Name { get; set; }

        List<Division> Divisions  = new List<Division>();
        public League(string name) //: base()
        {
            Name = name;
            Divisions.Add(new Division("DivisionA"));
            Divisions.Add(new Division("DivisionB"));
            Divisions.Add(new Division("DivisionC"));
        }
        private League()
        {
        }
    }
}

Objects: Division

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Collections.ObjectModel;

namespace Treeview01
{
    public class Division
    {
        public string Name { get; set; }

        List<Team> Teams = new List<Team>();
        public Division(string name) //: base()
        {
            Name = name;
            Teams.Add(new Team("Bear"));
            Teams.Add(new Team("Rocket"));
        }
        private Division()
        {
        }

    }
}

Objects: Team

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Treeview01
{
    public class Team
    {
        public string Name { get; set; }

        public Team(string name)
        {
            Name = name;
        }

        private Team()
        {
        }
    }
}

XAML:

<Window x:Class="Treeview01.Window1"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  Title="HierarchicalDataTemplate Sample"
  xmlns:src="clr-namespace:Treeview01">
    <DockPanel>
        <DockPanel.Resources>
            <src:ListLeagueList x:Key="MyList"/>

            <HierarchicalDataTemplate DataType    = "{x:Type src:League}"
                                ItemsSource = "{Binding Path=Divisions}">
                <TextBlock Text="{Binding Path=Name}"/>
            </HierarchicalDataTemplate>

            <HierarchicalDataTemplate DataType    = "{x:Type src:Division}"
                                ItemsSource = "{Binding Path=Teams}">
                <TextBlock Text="{Binding Path=Name}"/>
            </HierarchicalDataTemplate>

            <DataTemplate DataType="{x:Type src:Team}">
                <TextBlock Text="{Binding Path=Name}"/>
            </DataTemplate>
            
        </DockPanel.Resources>

        <Menu Name="menu1" DockPanel.Dock="Top" Margin="10,10,10,10">
            <MenuItem Header="My Soccer Leagues"
                  ItemsSource="{Binding Source={StaticResource MyList}}" />
        </Menu>

        <TreeView>
            <TreeViewItem ItemsSource="{Binding Source={StaticResource MyList}}" Header="My Soccer Leagues" />
        </TreeView>

    </DockPanel>
</Window>

XAML.CS:

using System.Windows;

namespace Treeview01
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
        }

    }
}

With the code above, only the first level data is represented, as the picture below.

https://i.stack.imgur.com/GXUS2.png

Please check and correct my code. Thank you very much!