The wedge is what determines what direction the tree will fall in. It compromises the integrity of the tree. The direction that the wedge is facing is where the tree will land.
First cut in a downwards direction about halfway into the tree. Your next cut should be perpendicular to the tree, and lastly upwards. Remove pieces of the wedge as you can. If you were to cut upwards first or second, your chainsaw would likely get stuck under the weight of the tree.