Creating a XAML special ContextMenu

Hi !

i'm just trying since 2 weeks to build a special contextMenu for my XAML Application.
The XAML code must be simple.
Let me describe it :
I have a treeview that contains buttons  in his treeViewItems.
I would like to show a contextMenu when i click (leftClick) on 1 of these buttons.
This contextMenu :
-will have the same width as the button it appears from.
-will have a transparent Background,
-will be over any other treeviewItem or components (like web layers),
-will have menu items composed of 1 icon and 1 Text (Menu Title).

I have tried with the "" component but it width never get 100% of his container (the button). I have the same pb with the "". The container Panel of an "Expander" component does not pass over other items.

If you have an idea i'llbe glad to read it!!

Thx 4 your help!!