A sapling is a young tree that has not yet reached its full size or maturity. A tree, on the other hand, is a fully-grown plant with atrunk and branches. Saplings are typically planted as seedlings, which means they have been grown from seeds in nurseries. Once they are old enough and big enough to be transplanted into the ground, they become saplings. Most trees take many years to reach their full height and width potential, though this can vary depending on the species.