Zoom feature - drill into a subnode

My use case is that I often expand nodes and focus on a subnode deep inside the tree. When you have a broad and deep tree, display is challenging within the confines of a portlet.

Is there a way to specify where in the whole treeData to start the top-level display? For example if a hierarchy within treeData is `a - b - c - ...n`, can you zoom in to only show from 'b' on down, or just from 'b' to 'c'?