If the tree is inside the tree that you want to keep, and is larger than the tree you want to keep, you need to cut it as far down as possible. The reason: as both plants mature, the additional tree will kill your Granny Smith both in growth and in siphioning the limited resources needed by the Granny Smith tree to survive. If you wait too much longer, the Granny Smith might be too far gone to save. -Birdy