In real trouble (2,1,4)
I believe the answer is:
up a tree
'in real trouble' 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" , "Like a lumberjack" , "In slangy difficulties, maybe on branch" , "In great difficulties, like the rackaby baby" .)