Stymied (2,1,4)
'stymied' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for up a tree that I've seen before include "American in need of assistance" , "In slangy difficulties, maybe on branch" , "Like a lumberjack" , "In great difficulties, like the rackaby baby" .)
(Other definitions for frustrated that I've seen before include "Disappointingly unsuccessful" , "Prevented from progressing" , "Foiled" , "Thwarted" , "Having a sense of discouragement and dissatisfaction" .)