Ruby class hierarchy

I was going to develop a tree view of ruby class hierarchy using the
FreeMind software. I was thinking of basing it on
http://www.insula.cz/dali/material/rubycl/ but I want to show pretty
much everything with Object in the middle then have types of Objects
branching off. So, for example, I would have branches on Object like
Object_Data_Types, Object_IO, Object_Exceptions, etc. Then on
Object_Data_types I would have branches like Numeric, Date, etc.

I think this would be useful, do you? Has this already been done?

Thank you.