It looks like it's still young so if you pruned the top hard, just leaving a few branches, it's possible you may get it to backbud lower on the trunk. If so you can use the new buds to grow branches more fitting a tree like form. If not, you're left with making bunjin stlye with the branches and foliage at the upper part of the tree. Also you could air layer the top and start over.

Tony