表示“在树上”时，凡是树上长出的东西用“on” 如：There are many apples on the tree. 苹果树上有一些苹果。

There are some leaves on the tree. 树上有一些树叶。 凡是落在、放在树上的用in Some birds are in the treeThere is a child in the tree. There is a cat in the tree.