Nothing sinister about tree (5)
I believe the answer is:
olive
'tree' is the definition.
(olive tree is a kind of tree)
'nothing sinister about' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'sinister' becomes 'evil' (similar in meaning).
'about' says the letters should be written in reverse.
'evil' back-to-front is 'live'.
'o'+'live'='OLIVE'
(Other definitions for olive that I've seen before include "Bitter fruit" , "woman" , "Greyish-green; fruit" , "Yellowish-green - fruit" , "Girl's name - colour" .)