[dastbe]

Do you give them a graph data structure or something that is explicitly a tree?

[dnautics]

A acyclic graph is isomorphic to a tree, but the way you access the vertices and edges is completely different.

[palunon]

Depends on your memory representation of the graph. If you simply use the obvious one (a node have a list of pointers to its successors), I don't see the difference except for successors[]/children[]

[dnautics]

You're right. I mentioned acyclic graph and my mind slipped to general graphs. Although often graphs are represented as say a sparse matrix.