You might be able to start at the top by making a series of increasingly larger V notches.Us either, Bruce, which is why for the past two years we have walked around it, mumbled a few choice swear words and walk away from it for a couple of months.
Somebody told us on another forum to notch it from the top stopping when it starts to close get the saw out of there. I'm dubious about that method. I've seen them pinch closed so fast you don't have time to jerk the chain saw blade out if the way.
I have 2 saws, a smaller Stihl MS180 and a larger Echo 590. After I got the Echo I've occasionally needed to use one to free up the other


That said, I have seen people who know what the heck they are doing use wedges to force a leaner to fall where they want it, against the lean, once the saw is far enough in a big tree to hammer wedges in. I've also seen them finish the drop by pulling the saw when the hinge is almost ready to break then hammering the wedges (always with the backside of an axe of course, real woodsmen don't carry a hand sledge like I do) to force the back side of the tree up enough to break the hinge.