C#のWPFでTreeViewへデータをバインドする

    public class TreeSource : INotifyPropertyChanged
    {
        private bool                             _IsExpanded = true;
        private string                           _Text       = "";
        private TreeSource                       _Parent     = null;
        private ObservableCollection<TreeSource> _Children   = null;


        public bool IsExpanded
        {
            get { return _IsExpanded; }
            set { _IsExpanded = value; OnPropertyChanged("IsExpanded"); }
        }

        public string Text
        {
            get { return _Text; }
            set { _Text = value; OnPropertyChanged("Text"); }
        }

        public TreeSource Parent
        {
            get { return _Parent; }
            set { _Parent = value; OnPropertyChanged("Parent"); }
        }

        public ObservableCollection<TreeSource> Children
        {
            get { return _Children; }
            set { _Children = value; OnPropertyChanged("Children"); }
        }



        public event PropertyChangedEventHandler PropertyChanged;
        private void OnPropertyChanged(string name)
        {
            if (null == this.PropertyChanged) return;
            this.PropertyChanged(this, new PropertyChangedEventArgs(name));
        }

        public void Add(TreeSource child)
        {
            if (null == Children) Children = new ObservableCollection<TreeSource>();
            child.Parent = this;
            Children.Add(child);
        }
    }

<Window x:Class="WpfApplication1.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:WpfApplication1"
        mc:Ignorable="d"
        Title="MainWindow" Height="200" Width="250">
    <Grid Margin="20">
        <TreeView ItemsSource="{Binding TreeRoot}">
            <TreeView.Resources>
                <Style TargetType="TreeViewItem">
                    <Setter Property="IsExpanded" Value="{Binding Path=IsExpanded,Mode=TwoWay}"/>
                </Style>
            </TreeView.Resources>
            <TreeView.ItemTemplate>
                <HierarchicalDataTemplate DataType="{x:Type local:TreeSource}" ItemsSource="{Binding Children}">
                    <TextBlock Text="{Binding Text}"/>
                </HierarchicalDataTemplate>
            </TreeView.ItemTemplate>
        </TreeView>
    </Grid>
</Window>

    public partial class MainWindow : Window
    {
        public ObservableCollection<TreeSource> TreeRoot { get; set; }


        public MainWindow()
        {
            InitializeComponent();

            TreeRoot = new ObservableCollection<TreeSource>();
            var item1  = new TreeSource() { Text = "Item1", IsExpanded = true };
            var item11 = new TreeSource() { Text = "Item1-1", IsExpanded = true };
            var item12 = new TreeSource() { Text = "Item1-2", IsExpanded = true };
            var item2  = new TreeSource() { Text = "Item2", IsExpanded = false };
            var item21 = new TreeSource() { Text = "Item2-1", IsExpanded = true };
            TreeRoot.Add(item1);
            TreeRoot.Add(item2);
            item1.Add(item11);
            item1.Add(item12);
            item2.Add(item21);

            DataContext = this;
        }
    }