Hi,
You could use the CustomCallback event on the ASPxTreeView/ASPxTreeList so you won't post the entire form. Otherwise take a look at the ASPxClientTreeView/ASPxClientTreeList to use javascript to get the inserted node, for example, you could use: AddNewRow(); and manage your inserted record from the client side and then use a CallbackPanel.
Take a look at:
ASPxTreeView[
^]
ASPxClientTreeView[
^]
Hope it helps.