I would agree with everything beenthere said, but, in addition, after you dig around it and cut a few roots, put your bucket up on the tree about 4' or 5' from the ground and push. Often, you can push on the tree a little higher up like this and get it to push over some. When it pushes over some, if things go good, it'll expose the roots (maybe even the tap root). Then, you can drop the bucket and get your cutting edge in there on the tap root, then curl up as beenthere described. If it doesn't pop loose, go to the other side and repeat this process. Keep working it back and forth cutting roots as you go. It'll finally turn loose.
Good luck,
BR