Sounds like a healthy cherimoya to me, its probably just growing too fast for its own good. Just use some support to make it upright. The reason you probably havenÂt seen much branching is because it hasnÂt lost much leaves yet. New branches actually grows right out of the leaf petiole, usually once the leaves drop. Rarely will you ever get see a bud growth above the leaf. Try it out, where you want it to branch, just cut the leaves. You could also cut the tip of the plant to get it to start branching. IÂm not sure where your at but depending on your climate you may want to wait till spring.
I have grown some to 5ft before it even branch out and this was plants in the ground.