You can throw a towel over a door and use it to do pullups, by the way. No need to find a tree branch. His evernote is much better than mine though, I'm such a lame pre-optimizer.
Won't the door be in the way? Or how exactly would this look? I would also be worried about breaking the door.
Open the door all the way until it hits the wall, throw a towel over it, and start doing pullups. Some people use workout gloves, but it's basically anything that will serve as padding. The door will hold, for sure.