I like MindNode (mind mapping tool) for iOS but the UI can be opaque. I couldn't figure out how to easily collapse a tree branch ("fold a node"); I had to dig through a painful menu every time. I knew there had to be a better way but the documentation and Google were no help.
There are two better ways.
1. In settings turn on the edit menu. Then when you tap a node you see an edit menu with 'fold' as a choice. (MindNode on Twitter told me that one)
2 If the edit menu is off in settings then tap once to select a node and then tap again to see the edit menu. (Don't double tap, that doesn't work.)
I hope this helps someone. Adding some terms to help with search: gesture, tap, iOS, MindNode, tree, branch, collapse, fold, close, iPhone.