I have to draw multiple inheritance type hierarchies. The worst case is something like the following:

I used tables and tree-dvipsto draw these figures, but I am now looking for something that is xelatex compatible.
I started typesetting simple hierarchies with forrest, but for cases like the one above this seems to be overkill. I already found Is there a library for drawing object inheritance trees in TikZ? but the problem is more complicated since inheritance may involve two or more parent nodes.
So: Is there a package for this or a predefined style for forest?
