Collapsing nodes (newbie question)
 

I'm evaluating OmniGraffle as a prospective mindmapping tool. Most mindmapping applications let the user collapse any node in the graph just by clicking it or taking some other simple action, thus allowing one to de-clutter a complex graph.

In OmniGraffle, this only seems possible by the very deliberate action of creating a subgraph (in Pro only!), and manually collapsing/expanding it through a contextual menu. Is there a simpler way of doing this sort of thing?

Thanks in advance,

Mike