As a treat I transpose a little melody (7)
I believe the answer is:
arietta
'a little melody' is the definition.
(I've seen this in another clue)
'as a treat i transpose' is the wordplay.
'as' becomes 'a' (I can't justify this - if you can you should give a lot more credence to this answer).
'transpose' is an anagram indicator (I've seen 'transposed' mean this).
'treat'+'i'='treati'
'treati' anagrammed gives 'rietta'.
'a'+'rietta'='ARIETTA'
Can you help me to learn more?
(Other definitions for arietta that I've seen before include "Little aria" , "number from opera" , "Short operatic song" , "Short operatic air" , "Short operatic number" .)