Rook flying out of unusually narrow tree (5)
I believe the answer is:
rowan
'unusually narrow tree' is the definition.
'rowan' can be an answer for 'tree' (type of tree). I am not sure about the 'unusually narrow' bit.
'rook flying out of' is the wordplay.
'rook' becomes 'R' (chess abbreviation).
'flying' becomes 'wan' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'out' is an insertion indicator.
'of' becomes 'o''.
'r'+'wan'='rwan'
'rwan' placed around 'o' is 'ROWAN'.
Can you help me to learn more?
(Other definitions for rowan that I've seen before include "The mountain ash tree" , "Mountain-ash" , "Red-berried tree" , "source of berries" , "-- Williams, theologian" .)