y do you need the leaves to face the camera ? In real life , the leaves don't face you when you look at them.That trick was used for sprites because they were only 2 planes, and if they didn't rotate to face the camera you would see they were a 2d plane image. For a tree made of a model with individual leaves , there is no reason to have them face the camera , in fact , doing so would look rather strange. A better idea would be for the leaves to have some kind of animation , just my 2 cents.