There are several synonyms for the phrase "hadst up a tree." One such synonym could be "stuck in a tree," indicating a situation where a person or animal is unable to get down from a tree they have climbed. Another similar phrase could be "trapped in a tree," again indicating a situation where someone is unable to get down due to being caught in the branches or the height of the tree. Additionally, "perched in a tree" could be used to describe someone or something sitting or standing on a branch or in a tree, but not necessarily stuck or unable to move.