With current version if RadMenuItem has been loaded you can use ItemsControl.ItemsControlFromItemContainer method. With next version of RadMenu you'll be able to
property and cast it to RadMenuItem to get the ParentItem of some RadMenuItem (next version is scheduled till the end of week).
Currently Silverlight 2 don't support adding UIElement that are in the visual tree to Tag
property. That is why you get "StackOverflow exception".
Why do you need parentMenuItem? What do you want to achieve?
You can see example on how to create menu from XML in our online examples here:
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