Ancient fruit-tree: it gets a bit of research in study (6)
I believe the answer is:
citron
'ancient fruit-tree' is the definition.
'it gets a bit of research in study' is the wordplay.
'gets' says to put letters next to each other.
'a bit of' indicates taking the first letters.
'in' is an insertion indicator.
'study' becomes 'con' (I've seen this before).
The initial letter of 'research' is 'r'.
'it'+'r'='itr'
'itr' inserted inside 'con' is 'CITRON'.
(Other definitions for citron that I've seen before include "Tree producing fruit" , "Large lemon-like fruit" , "It's like a lemon" .)