I would list the following as the minimal requirements for a safe tree climbing harness:
1. Waist belt with a life support quality closure/buckle
2. Leg straps with sufficient pressure distribution that a climber can sit in the harness with feet off the tree for at least 10 minutes. Things can happen very quickly in trees where you have to solve a problem and you can't get your feet on the tree, sometimes for a very long time.
3. All harness components and connections designed and fabricated to create life support quality for work positioning climbing.
For example rock climbing harnesses do not work for tree climbing and they are not safe for tree climbing. They are made to catch you if you fall on a high stretch rock rope. Tree climbing harnesses are called "work positioning" harnesses, which means that the climber weight is on the harness most of the time during a climb. Tree climber ropes are static or semi-static, either way very low stretch. That's why tree climbers say "We don't fall", the tree climbing system is not designed to catch falls, a climber can be seriously injured falling onto static rope in a tree climbing system.
All that said I applaud your efforts but strongly suggest you're approaching it from the wrong direction, a tree harness should have much more waist and leg support than a rock harness. Your harness is more minimal than a rock harness and is what I consider unsafe for tree climbing.
-AJ