Starter software on tree is wrong (9)
I believe the answer is:
appetiser
'starter' is the definition.
(I know that starter can be written as appetiser)
'software on tree is wrong' is the wordplay.
'software' becomes 'app' (software application).
'on' indicates putting letters inside.
'wrong' is an anagram indicator.
'tree'+'is'='treeis'
'treeis' anagrammed gives 'etiser'.
'app' going into 'etiser' is 'APPETISER'.
(Other definitions for appetiser that I've seen before include "Small starter dish" , "Relish" , "Hors d'oeuvre" , "preprandial treat" , "Antipasto" .)