this is assuming that you have the tree cut down to the ground with the stump level to the ground. If you do not, then you should do so.
Then get a 1/2 inch heavy duty drill and get a 1 1/2 inch paddle bit or spade bit and drill deep and numerous holes in the stump. Then pour karo syrup in the holes and do this when ever it is dry of this syrup. Eventually, and don't be in a hurry, the tree will decay out faster for you. The sugar works just like it does on your teeth.