expand one node at a time in treeview

To anyone who know how to accomplish this: 
I have a tree view like this:
1.
1.1
1.2
2.
2.1
2.2
....
what I want to accomplish is when user click a parent node (for example node 1) every other parent nodes are collapse except the selected node( node 1), in other word, only one subtree is expanded at a time.
Thank you very much!
 
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