noun · a digital space or social media account where people can post secrets or vent anonymously

很多人在学校的树洞里吐露心声。

a person who listens to one's private thoughts or secrets without judgment

谢谢你一直当我的树洞，听我抱怨这么多。

a hole or cavity in the trunk of a tree

小松鼠在树洞里藏了很多坚果。