i have seen some the size of crapemyrtles, probably 15'-20' tall, and pruned to a similar shape with the lower branches removed, giving it a more tree-like shape.
that is the way i am growing mine but it has not reached those proportions yet.
you can keep it smaller by pruning it into a more compact form but they are more attractive, in my opinion, when allowed to grow taller. the flowers cover the ground beneath the branches with pink petals.

Thanks Jeff.
I think because of the way this one grows it would look nice in a tree shape like that. I'd like to do mine that way too.
I've had the poor thing ina pot for 2 years now and really have to get it in the ground just can't decide where.