Complete changes in tree (6)
I believe the answer is:
entire
'complete' is the definition.
(synonyms)
'changes in tree' is the wordplay.
'changes' indicates an anagram.
'in'+'tree'='intree'
'intree' anagrammed gives 'ENTIRE'.
(Other definitions for entire that I've seen before include "Whole; unbroken" , "Utter" , "Complete, intact" , "Whole and complete" , "everything" .)