核心问题
（1）He's picking the apples on that tree.
(2) He is in that tree.
请问 on the tree 与 in the tree 都是“在树上”的意思, 它们有无区别?
词典解答
可以这样来记: 当人或鸟在树上时, 通常用 in the tree, 但有时也用 on the tree; 而树叶、果实等在树上时, 用 on the tree。但是, 当强调鸟在树的表面时, 也可以使用介词 on:
A bird had settled on a tree close to where I was standing. 一只鸟落在一棵离我站的地方很近的树上。