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 "<Menu>" component but it width never get 100% of his container (the button). I have the same pb with the "<ContextMenu>". 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!!