Mr Atkinson's tree (5)
I believe the answer is:
rowan
'tree' is the definition.
(type of tree)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for rowan that I've seen before include "Red-berried tree" , "-- Williams, theologian" , "Tree - archbishop" , "Tree bearing bright red berries" , "Mr Atkinson, actor" .)