Squirrel's treat (5)
I believe the answer is:
acorn
'squirrel's treat' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for acorn that I've seen before include "fruit in a cup" , "Source of a great oak" , "Tree seed" , "cup's content" , "From which a tall tree may grow" .)