Me - I would wait until they are a little bigger, they look bit small yet. But if you don't want them any taller - you could take the tips off where you want the branching to start. If you cut farther down than the tip -then look for a node in the direction you would like a new branch and cut just above that node on a horizontal angle( flat across). If you are in an area where rot might be an issue, then either seal the tip or dab it with some cinnamon to help it dry faster.