The phrase "hast up a tree" refers to someone who has quickly climbed up a tree, most likely to escape danger or to retrieve something. Synonyms for this phrase can be "climbed up a tree hastily," "scaled a tree quickly," or "ascended a tree promptly." Other words that can be used to describe this action include "climbed up rapidly," "scampered up," or "scaled swiftly." No matter which synonym is used, the meaning is clear that the person has hastily climbed up a tree for a specific reason, often out of necessity.