“Gum” you may know. It refers to a number of things (encía, goma, pegamento, resina).
Were you to climb a gum tree (árbol de goma, árbol gomero) or a eucalyptus (eucalipto) tree you might get stuck (es posible que se quede atascado). Why? The tree emits a type of gum.
So, if someone is “up a gum tree” that person is in a very difficult position, perhaps with few options for action. Perhaps in Spanish you would say “estar en un aprieto”. An example:
- Mr. Sanchez is up a gum tree about what to do about Catalunya.
There is also a phrasal verb: to gum up the works.
If someone “gums up the works” it means that an planned action or process, usually through stupidity or blundering (torpe), is stopped, frustrated, or cannot function owing to some serious complications. Perhaps a similar expression in Spanish would be “meter un palo en la rueda”.