Cuckoo saw tree top (7)
I believe the answer is:
sweater
'top' is the definition.
(type of top or jumper)
'cuckoo saw tree' is the wordplay.
'cuckoo' is an anagram indicator (I've seen this in other clues).
'saw'+'tree'='sawtree'
'sawtree' is an anagram of 'SWEATER'.
(Other definitions for sweater that I've seen before include "Knitted upper garment" , "Wear" , "A present from Mum!" , "Jersey may become" , "Jumper (7)" .)