How to straighten a frame?

Why not search for a good frame? Your propane torch will not give enough heat. The tree idea is not good it needs to be pulled and precisely jerking it will not bend it back to where it belongs. It has to be pulled in the proper direction to be usable. If you don't want to take it to a frame shop I would try to fine a frame off another truck and swap it out but its hard work and a lot of time. Craig's list is a good start. Good luck!