OK, say you got a big tree on the ground. Well fiorst, you can cut junk logs nearby and lay them out for the eventual big tree main stem to land on.
OK2, either way, say you have the main stem on the ground. In the smaller branch wood while bucking that, cut off with slanty cuts, like at a 45. Then go your regular cut size and do a regular 90. Now you have a round which is flat on one side to hit with the sledge, the other side is beveled at an angle to help get it started under the main log. Stick it where you want it and wail away.
Procedure to get lift wedges two at a time:
Cut square, then one slanty cut, then cut square going down an appropriate sized branch, gives you two wedges. Repeat as necessary to get you all the wedges you want, and you can start with around a 3-4inch one, go bigger if necessary, but they get harder to hammer in. You can make the slanty cut side longer and a sharper angle if needed over a 45 of course.
I----/----I See?