Wife of villain I spotted in a fruit tree, climbing (6)
I believe the answer is:
emilia
'wife of villain' is the definition.
(wife of Iago in Shakespeare's Othello)
'i spotted in a fruit tree climbing' is the wordplay.
'spotted in' means one lot of letters goes inside another.
'fruit tree' becomes 'lime' (lime is a kind of fruit tree).
'climbing' shows that the letters should be reversed in order (in a down clue, letters climb up).
'a'+'lime'='alime'
'i' placed into 'alime' is 'ailime'.
'ailime' reversed gives 'EMILIA'.
(Other definitions for emilia that I've seen before include "- - Fox, film actress" , "Wife of Iago (Othello)" , "Italian girl" .)