It can be challenging to come up with synonyms for the phrase "hast up tree," as it is a relatively specific and uncommon expression. However, some possible alternatives might include "climbing a tree," "scaling a trunk," "ascending a branch," or "scrambling up foliage." Each of these phrases conveys the idea of climbing a tree, but with slightly different nuances or connotations. For example, "scaling a trunk" may suggest a more deliberate and careful ascent, while "scrambling up foliage" implies a more haphazard or improvisational approach. Ultimately, the best synonym will depend on the specific context and intended meaning of the phrase.