look for the BSP DEBUG item in the tree. you can simulate collisions with a point and it will only draw the bboxes that are pertinent to that collision test. and you can limit how deep it goes into the recursion with the depth parameter.
one thing I've noticed with it is the sortnorms seems to fill up the same voluem for the most part, over and over, 50% seem to have a edge at the center, for example, most pofs, you don't see them pile up right on top of each other like that. it also seems like child bounding boxes go a lot further outside the parent than they should, like there will be a bounding box that covers everything on the right, then the child of thab box will have everything in the middle (both left and right)