I have one in a pot in my greenhouse, and I cut it too tall the first time and had problems with the branches hitting the ceiling of the greenhouse. I would cut it about a fourth of the intended height (so if you have an 8 ft ceiling, cut it at 2 ft, if you have a 10 ft ceiling, cut it at 2 1/2 ft etc. Then when it branches, cut each branch down to about 1-2 ft, and you should get a nice canopy. Now that mine has hit the ceiling, I let the branches go, and they drape down for a nice effect.
Also, in case you didn't know, when it blooms, the berries are actually edible!
Should mention, my tree is ten years old and in about a 20 gallon pot. They do not like much nitrogen fertilizer, and I have burned mine a few times. Also, be careful when pruning that you can actually see the whole branch, because I have accidentally cut off blossom clusters before, because I couldn't actually see the top of the canopy...
Cheers,
Carolyn