North Dakota's right about tree (6)
I believe the answer is:
linden
'tree' is the definition.
(I know that linden is a type of tree)
'north dakota's right about' is the wordplay.
'north dakota' becomes 'ND' (abbreviation for the US state).
'right' becomes 'lien' (legal right).
'about' indicates putting letters inside.
'nd' inserted within 'lien' is 'LINDEN'.
(Other definitions for linden that I've seen before include "One twigged" , "Lime tree" , "Tree with Lea - also called 8" , "Unter den ------, iconic boulevard in Berlin" , "type of tree" .)