How to get a call relationship of an open solution using a plugin

Question

I am trying to develop a VSPackage for VS 2010 that examines all available methods in the current solution and restores the invocation relationships of each individual method, as the built-in VS Call Hierarchy function does.

I managed to get all the available type names and its members in the solution using the DTE automation object, moving from the solution to its projects, project classes / types and class members (most importantly its methods), however Im not able to restore the calling relationship. I did not find any VS / VS SDK service that could help me. Any clues?

Thanks in advance!