More mature tree (5)
I believe the answer is:
elder
This clue is a double definition.
'more mature' is the first definition.
(older or more mature)
'tree' is the second definition.
(elder is a kind of tree)
(Other definitions for elder that I've seen before include "Senior - church official" , "Tree; of greater age" , "Berry-bearing shrub" , "Church official; tree" , "Senior leader" .)