WPF Tree多级绑定

<Window x:Class="TreeTest.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:TreeTest"
        mc:Ignorable="d"
        Title="MainWindow" Height="650" Width="400">
    <Grid>
        <Grid.Resources>
            <HierarchicalDataTemplate DataType="{x:Type local:Node}" ItemsSource="{Binding Nodes}">
                <StackPanel Orientation="Horizontal" Margin="0,2,0,2">
                    <!--<Image Source="pack://application:,,,/WpfTest;Component/Resources/KnowDot.png" Width="16" Height="16" />-->
                    <!--<Image Source="Resources/KnowDot.png" Width="16" Height="16" />-->
                    <Image Source="/TreeTest;Component/Resources/KnowDot.png" Width="16" Height="16" />
                    <TextBlock Text="{Binding Name}" ToolTip="{Binding Name}" Tag="{Binding}"/>
                </StackPanel>
            </HierarchicalDataTemplate>
        </Grid.Resources>
        <Grid.RowDefinitions>
            <RowDefinition/>
            <RowDefinition Height="150"/>
        </Grid.RowDefinitions>
        <TreeView Name="TreeView"/>
        <TextBox Grid.Row="1" DataContext="{Binding ElementName=TreeView, Path=SelectedItem}" Text="{Binding Desp, Mode=TwoWay}">
            
            
        </TextBox>
        <Button Grid.Row="1" Width="100" Margin="282,10,10,-10" Click="Button_Click"></Button>
    </Grid>
</Window>

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

namespace TreeTest
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        List<Node> outputList = new List<Node>();
        public MainWindow()
        {
            InitializeComponent();
            List<Node> nodes = new List<Node>()
            {
                new Node { ID = 1, Name = "中国" },
                new Node { ID = 2, Name = "北京市", ParentID = 1, Desp = "北京描述" },
                new Node { ID = 3, Name = "吉林省", ParentID = 1, Desp = "吉林描述"  },
                new Node { ID = 4, Name = "上海市", ParentID = 1 , Desp = "上海描述" },
                new Node { ID = 5, Name = "海淀区", ParentID = 2 },
                new Node { ID = 6, Name = "朝阳区", ParentID = 2 },
                new Node { ID = 7, Name = "大兴区", ParentID = 2 },
                new Node { ID = 8, Name = "白山市", ParentID = 3 },
                new Node { ID = 9, Name = "长春市", ParentID = 3 },
                new Node { ID = 10, Name = "抚松县", ParentID = 8 },
                new Node { ID = 11, Name = "靖宇县", ParentID = 8 },
                new Node { ID = 12, Name = "美国" },
                new Node { ID = 13, Name = "南美洲", ParentID = 12},
                new Node { ID = 14, Name = "纽约", ParentID = 13 },
            };
            // 绑定树
          outputList = Bind(nodes);
            //(TreeView.SelectedItem as Node).ID
            this.TreeView.ItemsSource = outputList;
        }
        /// <summary>
        /// 绑定树
        /// </summary>
        List<Node> Bind(List<Node> nodes)
        {
            List<Node> outputList = new List<Node>();
            for (int i = 0; i < nodes.Count; i++)
            {
                if (nodes[i].ParentID == -1)
                {
                    outputList.Add(nodes[i]);
                }
                else
                {
                    FindDownward(nodes, nodes[i].ParentID).Nodes.Add(nodes[i]);
                }
            }
            return outputList;
        }
        /// <summary>
        /// 递归向下查找
        /// </summary>
        Node FindDownward(List<Node> nodes, int id)
        {
            if (nodes == null) return null;
            for (int i = 0; i < nodes.Count; i++)
            {
                if (nodes[i].ID == id)
                {
                    return nodes[i];
                }
                Node node = FindDownward(nodes[i].Nodes, id);
                if (node != null)
                {
                    return node;
                }
            }
            return null;
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            int a = 3;
        }
    }

    public class Node
    {
        public Node()
        {
            this.Nodes = new List<Node>();
            this.ParentID = -1;
            Desp = "描述";
        }
        public int ID { get; set; }
        public string Name { get; set; }
        public int ParentID { get; set; }
        public string Desp { get; set; }
        public List<Node> Nodes { get; set; }
    }
}