Twig is found in drink under middle of tree (7)
I believe the answer is:
realise
'twig' is the definition.
('twig'->'realize' is in my internal thesaurus and 'ize'->'ise')
'is found in drink under middle of tree' is the wordplay.
'found in' means one lot of letters goes inside another.
'drink' becomes 'ale' (ale is a kind of drink**).
'under' says to put letters next to each other.
'middle of' says to take the centre.
The centre of 'tree' is 're'.
'is' going within 'ale' is 'alise'.
'alise' put after 're' is 'REALISE'.
(Other definitions for realise that I've seen before include "appreciate" , "Come to conclusion" , "Convert (asset) into cash" , "Understand - cash in" , "See the light" .)