Fanatic say gets married in tree (6)
I believe the answer is:
nutmeg
'tree' is the definition.
(nutmeg is a kind of tree)
'fanatic say gets married' is the wordplay.
'fanatic' becomes 'nut' (I've seen this before).
'say' becomes 'eg'.
'gets' is an insertion indicator (gets can mean captures or absorbs).
'married' becomes 'm'.
'nut'+'eg'='nuteg'
'nuteg' placed around 'm' is 'NUTMEG'.
'in' acts as a link.
(Other definitions for nutmeg that I've seen before include "Fragrant seed of tropical tree grated as spice" , "Kernel and girl for a spice" , "Aromatic seed - met gnu (anag)" , "Men gut this herb badly" , "Asian tree whose aromatic seed is used as spice when grated or ground" .)