Wedges are hard to make once the saw is stuck.....
I'd cut that particular one the opposite way, cut 1/4 - 1/3 the way from top to bottom, then finish going bottom up. As the pressure is put on the cut, it opens the bottom up.
Ones that get hung up like that, I'll cut in 3-4 foot sections from the butt to the top of the tree, that way I'm not dodging larger pieces as they drop.