Like Johnp33, I cut up from the bottom, but usually I cut in stove lengths or 2x stove lengths. The less you alter the weight and distribution of weight with each cut, the less wild the resulting action is going to be. Once in a while, you get one that will teeter up after you get enough weight out of the lower end, and they can slide down with pretty good force after cutting off a section, so keep your chin and toes out of the way.
With any chainsaw cutting, paying real close attention to the pressures in all directions, side to side, up, down, is important. Watch the saw kerf like an eagle and look up a bit too. If it feels shaky, back off and re-evaluate your plan of action. Dragging out with a long rope or chain is probably always safer.