Anytime you are shooting at an extreme angle, either uphill or downhill, you need to account for the bullet hitting higher than it would on level ground. This is probably not a huge deal with a 60 yard shot out of a treestand - but all bullets start dropping the moment they leave the muzzle. We adjust our sights to account for this, and the line of the bore is pointing "uphill" when the sights are level. At distance, this can be a significant issue. There are volumes of stories from sheep hunters who shot over animals, either uphill or downhill, that they would have hit on level ground.