Native is right on. I'd also caution, for young trees, overpruning is a bigger danger than not pruning enough. Young trees need to be allowed to grow, and pruning is mostly to shape them, not to remove excess material, totally different than old trees, where the shaping is mostly complete and pruning is to remove most of the excess growth from the year before. When young trees grow long whips and start to seem top heavy is when they need a good pruning, but only prune the long whips about halfway back. Rule of thumb for trimming, other than the main leader and scaffolding growing off the main leader, if a branch grows out the top or bottom of a limb you cut it off altogether and the branches growing out the side of a limb are left to grow new limbs, only trimming the ends off of them if they are long and thin.