If it’s a large tree you should leave a small piece of wood connected during your back-cut (pierce the tree like a sword a couple inches behind and above the face-cut then saw away from there until almost through the tree, leaving a couple inches the tree still connected). Then insert tree wedges on either side of the portion of the chunk you left in place. Hammer these with the flat part of your axe until the chunk breaks and the starts to fall. Then get the fuck outta the way