Considering mindmapping some studying material and topics for my job.

There are a couple of broad topics and the content of each topic can go pretty deep. Each topic structured in such a way that I could make layers for each topic which would correspond with the depth of other topics. As such I thought it could be interesting to map the layers, and the detail of each layer - however far it goes - as depth (z axis if you will)... if that makes any sense?! What would be most important for me is that I could insert documents in the different topics... So I guess it would be rather extensive, almost database like.

As such, I was wondering if anyone had experience with 3d mind mapping software. I had a quick look and there don't seem to be too many products out, or none that seem particular striking. Any suggestions? Or do you have some good mind mapping experience and think the whole 3d thing would be a waste of time?