how to Add TreeViewItems into temporary TreeView in wpf?

Hi folks,

             I have a TreeView with 3 Items in my User Interface.

I want to Add One more TreeViewItem in the TreeView as First item.

so my logic is just Adding all 3 Items to one Temporary TreeView , then clear all items in my treeview, then Add my new Item then Add all 3 items from Temporary treeview.

is that logic good?

Problem is i am not able to Add these 3 Items into Temporary TreeView.

I am getting error like"Element already has a logical parent. It must be detached from the old parent before it is attached to a new one."

any one have idea?