添加MenuItems时XamlParseException未处理

在实现这个问题的答案时，我遇到了XamlParseException运行时错误。

我会解释错误是什么时候发生的，因为这对我来说没有任何意义。首先，我使用上一个问题的解决方案来构建两个Context Menus，当用户右键单击TreeViewitems时就会出现。

编辑：为了更好地理解，我将准确地发布代码。在将代码切换到这个位置后，我仍然收到错误。

public static TreeViewItem item1 = new TreeViewItem();
public static TreeViewItem item2 = new TreeViewItem();
ContextMenu item1_CM = new ContextMenu() { Background = Brushes.White, BorderBrush = Brushes.Black, BorderThickness = new Thickness(1) };
        MenuItem add1 = new MenuItem() { Header = "Add..." }; //Add & Delete MenuItems
        MenuItem delete1 = new MenuItem() { Header = "Delete..." };
ContextMenu item2_CM = new ContextMenu() { Background = Brushes.White, BorderBrush = Brushes.Black, BorderThickness = new Thickness(1) };
        MenuItem add2 = new MenuItem() { Header = "Add..." }; //Add & Delete MenuItems
        MenuItem delete2 = new MenuItem() { Header = "Delete..." };
public constructor()
{
     Tree = new ObservableCollection<TreeViewItem>();
     Tree.Add(item1);
     Tree.Add(item2);
     //Add MenuItems to TreeView ContextMenus
     item1_CM.Items.Add(add1);
     item1_CM.Items.Add(delete1);
     item1.Items.Add(item1_CM);
     item2_CM.Items.Add(add2);
     item2_CM.Items.Add(delete2);
     item2.Items.Add(item2_CM);
}

我为两个TreeViewItems加上两个MenuItems，就像这样。如果我编译并运行第一个集合，程序运行良好，但在将新的MenuItems添加到另一个TreeViewItem之后，我会得到XamlParseException was unhandled错误。是什么原因造成的？

谢谢你的帮助。

XAML根据请求

<Window x:Class="CircularButtonPrototype.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:sys="clr-namespace:System;assembly=mscorlib"
    xmlns:cmp="clr-namespace:System.ComponentModel;assembly=WindowsBase"
    Title="Window1" MinHeight="685" MaxHeight="685" Height="685" MinWidth="1044" MaxWidth="1044" Width="1044" AllowsTransparency="False" WindowStartupLocation="CenterScreen" WindowStyle="None" Visibility="Visible">
</Window>

我在XAML:中的TreeView

<TreeView Name="Tree_One" ItemsSource="{Binding Tree}" HorizontalAlignment="Left" Background="White" SelectedItemChanged="Tree_One_SelectedItemChanged" />

 item1.Items.Add(item1_CM);
 ...
 item2.Items.Add(item2_CM);

item1.ContextMenu = item1_CM;
...
item2.ContextMenu = item2_CM;

    public ObservableCollection<TreeViewItem> Tree { get; set; }
    public static TreeViewItem Item = new TreeViewItem {Header = "MainTreeViewItem"};
    public static TreeViewItem Item2 = new TreeViewItem {Header = "MainTreeViewItem"};
    ContextMenu contextMenu = new ContextMenu { Background = Brushes.White, BorderBrush = Brushes.Black, BorderThickness = new Thickness(1) };
    MenuItem addItem = new MenuItem() { Header = "Add..." }; //Add & Delete MenuItems
    MenuItem deleteItem = new MenuItem() { Header = "Delete..." };
    public MainWindow()
    {
        Tree = new ObservableCollection<TreeViewItem>();
        //Add MenuItems to TreeView ContextMenus
        contextMenu.Items.Add(addItem);
        contextMenu.Items.Add(deleteItem);
        Item.ContextMenu = contextMenu;
        Item2.ContextMenu = contextMenu;
        Tree.Add(Item);
        Tree.Add(Item2);
    }