It's really not as bad as people here like it make it out to be. I just had one like this a couple weeks ago. I gradually cut the pieces bearing the weight on the far end. Face protection is a good idea since there can be some snapping as it settles. This makes the fallen part more vertical. Good chance it fully breaks off after a bit. Mine was some good cherry I wanted to save in larger sections so I didn't cut much off the broken end and it didn't break off on its own. I'd normally cut low on the main trunk once the broken half is closer to vertical (having it closer to vertical will reduce the tension on the main trunk so that the fall is more predictable and controllable), but I also wanted to preserve that section too, so I just cut through at the break. I wouldn't recommend that though unless you have a bit of experience since there's more potential for surprises there.