My question did not refer to pruning for a tree as opposed to a bush. We know how to do that. We need to know how to eliminate the growth (suckers?) at the base of one tree. The other tree does not have this problem.
Certified GKH Gardening Expert
Perhaps, this article on Tree Sucker Control will help: https://www.gardeningknowhow.com/ornamental/trees/tgen/tree-sucker-removal-and-tree-sucker-control.htm