I just noticed the post, kind of late... Do a search on cutting heavy leaner trees, and barber chair like mentioned before.
Leaning trees can be real dangerous. It is usually recommended to do a plunge cut to relieve the center of the tree. then notch it, then fell it by cutting backwards out of the plunge cut.
I did a terrible job of trying to explain.
Anyway I like to got my head took off several years ago by a leaning tree splitting and shooting right back inches from my head.