Add menuitem When item source set to menuitem

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C#

WPF

Hello ,
I have created context menu and set its submenu item to an item source,But now I want to add one more menuitem as "Default".I do that exception is thrown as

Items collection must be empty before using ItemsSource.

Following is my code

MenuItem Menu1 = new MenuItem();
Menu1.Header = "Menu1";
MenuItem Menu2 = new MenuItem();
Menu2.ItemsSource = to some object collection;
Menu2.DisplayMemberPath = "Name";
Menu1.Items.Add(Menu2);

Now I want to add one more Item in Menu2 and the itemcollection
Already tried

MenuItem DefaultMenu = new MenuItem();
DefaultMenu.Header = "Default";

Menu2.Items.Insert(0, Default);

Throws exception
Is there any easy way to add another menuitem whose item source is already fixed

Thanks in advance