Sections at the top which now are free of bark will later become voids in the final product.
Paper drawings can be helpful but I like to work right on the wood. Here are considerations in marker.
After a few cuts it is evident that more needs to come off the sides. Marks like this are helpful as much of the lower material will be left in place as the interior cuts begin so as to leave a stabilizing mass that will help to absorb vibration. The lines help to visualize the final look and thus the amount that needs to be cut away inside.
As I cut through the upper section I hear a slight ticking. The Oland tool has made short work of a nail.