When felling trees, Plan A has the tree falling right where you want it to go. Once you hang one up, though - and even the best of us do - the game changes and it's time for Plan B. If you've got the equipment, you could just put a chain around the bole and pull, but the following trick may work if a chain's not handy. It's especially helpful if you are cutting sawlogs, because if it works, it will keep the valuable butt log intact. The one catch is that the tree needs to still be attached to the stump for this to work.
Start by taking a good look at your tree and how it is hung up. You'll have to make a decision: Are you going to try to make the tree move to the left or the right? A lot of this will depend on where your tree is relative to the main stem of the tree it is stuck in. Generally, you will want to try to move your hung tree away from that main stem.
Once you've determined the direction you want to go, the next step is to saw an undercut notch into the stump under your semi-felled tree at three- or nine-o'clock (assuming your half-felled tree is at noon). Make the bottom or slanted cut of the notch first, cutting up until you reach the hinge wood, then cut out the section of hinge above your undercut. This type of notch is known as a Humboldt notch, and is commonly used on large diameter trees in the west. Your undercut notch face should be angled toward the direction you want the tree to fall or roll in, and should go nearly halfway through the stump. If your hinge sheared or is largely broken, make the cut carefully and set wedges as you go to keep your bar from getting pinched.
Creating the undercut notch removes wood that is helping to support the tree and places the remaining section of the hinge under tension. Next, cut the remaining hinge wood starting at the back behind your new undercut hinge. Depending on how the tree is balanced, it may just slide off the stump or it may twist. It may also stay put, but with half of the original supporting wood and all of yoru hinge now gone, just a little bit of leverage should get the tree off the stump. If it hasn't come down by the time it slides off the stump, then it is probably time for Plan C. But that's another column.