RE: Shooting from tree
Bending at the waist will keep your anchor points in the correct place, which ensures your aim is the same as if you are shooting on the ground.
If you are taking a shot from an elevated position and you drop your bow arm and raise your string arm to adjust for the angle, your shot will be off. However, if you bend at the waist - keeping your bow arm straight, your string arm in place, and all your anchor points in all the correct positions, your aim will be the same and the shot will be the same as if you were shooting from the ground. Get out there and establish your anchor points and become very familiar with the way they feel. Get a feel for where your knuckles touch your ear or jaw bone and how your nose touches the string. Kisser buttons also help a lot.
You need to practice shooting from your stand, a lot. The set up, the draw, the aim, the everything feels completely different. Best way I know to duplicate a true "hunting" scenario is torun a few laps around the yard to get your heart beating fast. Then try to draw your bow and make a controlled shot.