"Up a tree" is an idiomatic expression that means being in a difficult or challenging situation where there seems to be no easy way to resolve an issue. It is often used to describe a state of feeling trapped or confounded. There are several synonyms for "up a tree" which include in a bind, in a quandary, cornered, in trouble, at a loss, in a fix, between a rock and a hard place, and in a pickle. These synonyms imply a situation where one feels they have exhausted all their options and are unable to find a clear way forward. They can be used interchangeably with "up a tree" to indicate a state of frustration and confusion.