What do you mean by "SERVER SIDE"?
You interact with FlyTreeView at client side. Then you do postback. All client-side changes (including move/insert/select/check/expand/etc.) are repeated one by one at load-post-data stage.
At the same time all related NodeXXXX events are fired one by one.
So in this case you do not have any SERVER SIDE changes, since these events are fired before Page_Load (not as usual as any other events do).