That plant is always going to be more of a pyramidal form or at least taller than it is wide. However It will get to be 20+ feet wide in time. Prune away lower branches when they reach about an inch in diameter. Allowing them to grow larger if they are not to be permanent just takes energy from the tree that could have gone into permanent limbs. Prune primarily in late winter, with some minor triming in early summer if need be. Don't prune after about mid to late summer. How high you prune the limbs up from the ground is up to you.
The following web site gives more info and photos of this plant.
Thanks for the question. Please stop in again soon!
Q&A Library Searching Tips