Broken Maple Tree

GrassyKnoll

When I moved into a new house, last summer, a maple tree had been left in a pot by the previous owner. The trunk has clearly been snapped and is only about 6 inches tall.

I did nothing with it last year and it sprouted a few leaves in the pot.

This year, I planted it in the garden and the leaves/ branches are quite wispy but maybe 2 feet long. 

I guess the trunk is never going to grow longer, but I wonder if these 'branches' could get thicker if left. 

Is there anything I can do to help it?