Never, never, never put a lot of tension on that cable with anyone near it!
Here's what can happen--a leaning tree is like one with tension on a cable:
[ame=http://www.youtube.com/watch?v=2YAf61zz5VU]Falling a tree gone wrong (Barber chair) - YouTube[/ame]
Imagine what would happen to a tractor with a bucket up against the tree when it splits and pops?
I am not a faller, but here are some basics:
The wedge sets the direction. The wedge should be no deeper than 1/3 to 1/2 the diameter. If there is a lean, and you are trying to fall the tree in the direction of lean, cut a smaller wedge.
The back cut is done a couple inches higher then the apex of the wedge. That's to make a step so that when the tree falls, the step keeps it from kicking back. When limbs hit, it can still kick back, but it won't come off the stump until them.
The hinge, the wood between the back cut and the wedge, controls the fall to make sure the tree falls in the direction of the wedge. Both sides of the hinge should be parallel. If it's narrower on one side than the other, then when the tree starts to go it can break where the hinge is narrow and pivot.
I have used cables on leaning trees, but I only put a little tension on the cable before I finish cutting--mostly to make sure it is tight enough to be sure it won't come back and pinch the bar. If the tree diameter is large enough, I put falling wedges in the back cut to make sure it won't fall that direction and to help the cable. Then I start to pull it over with a come along and cable anchored to another tree or stump. I pull it up, then over in my direction (my cable is longer than the tree height by a safe margin). If it doesn't go, then I release most of the tension before going back and cutting the back cut a little deeper, then pull again. So far, it's worked every time and there have been no heart attack moments. Trees were 12-14" in diameter and 55-60 ft. tall.
No pickup and no tractor needed, no racing ahead when the tree starts to go and from where I am jacking with the come along I can watch the top of the tree.
I cut 6 trees leaning toward my house, all fell about where I wanted.
As I said, I am not a faller, so think it through before copying my method. The cable will keep the tree from falling backward--after all you have it guyed on one side with your cable. Just don't put a lot of tension on the tree before cutting. Remember the video. A lot of guys have been killed by barber chairs.