Scottish tree, one added to line (5)
I believe the answer is:
rowan
'scottish tree' is the definition.
'rowan' can be an answer for 'tree' (type of tree). I'm unsure of the 'scottish' bit.
'one added to line' is the wordplay.
'one' becomes 'an' (an apple is one apple).
'added to' is a charade indicator (letters next to each other).
'line' becomes 'row' (a row or line of things).
'an' put after 'row' is 'ROWAN'.
Can you help me to learn more?
(Other definitions for rowan that I've seen before include "Mountain-ash" , "Tree with orange-red berry-like fruits" , "The mountain ash tree" , "Tree bearing bright red berries" , "source of berries" .)