There isn't such a feature for RadTreeView.
My suggestion is to implement it the following way:
- in each node collection the last node, to be with Text "More..." and handling the ClientNodeClicked event to detect whether this particular node has been clicked. Then you need to call a script service with information of the requested page of nodes. The WebMethod in this service can return a RadTreeNodeData array which will be serialized to JSON. When the assigned callback (you should assign callback to the web service request) is called, you can iterate through the received RadTreeNodeData and create new nodes and insert them just before the "More..." - named node.
I hope this is helpful for you.
the Telerik team