If you are binding the data to the TreeView through a datasource this will probably involve a lot of javascript to get the functionality. I would recommend that you read through the
client-side API. What you could do would be to find the parent node that you are interested in finding, and then gather a collection of the child nodes of this node and add it to the new node that you want to show off the hierarchy of.
You could also potentially re-create the hierarchy in your database (might be easier), but it all depends on where your preference in creating this behavior lies.