Need help with my son's apple tree
 

My son planted some seeds when he was in kindergarten and he grew this tree in the house for a few years. Now when we decided to plant it outside, I discovered we should have been a little more educated of its care and pruning. It has two main leads with the one on the left more verticle and has branching up. The other one has more leaves along its lead stem making me think it will branch better. The question is, which one do I keep, which one do I prune?

If someone can tell me how to post the picture, I can do it.

Thanks