The few times I played paintball, I got the most kills at once while in a tree... it really depends on the situation and how much concealment the tree in question provides. Basically, I was hidden enough in the tree that if I didn't move, no one would see me. So, I waited till a group of 3 people walked past the tree. Shot them in the back and then proceeded to climb down. I figured if there was anyone else around, they know where I am now, but luckily there was no one and I was able to go find another hiding place
So, like I said, it depends on the situation. It's generally regarded as not the best place to be for shooting. If you're just spotting though, maybe not so bad.