Some complain a workman's climbing tree (5)
I believe the answer is:
rowan
'tree' is the definition.
(type of tree)
'some complain a workman's climbing' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'climbing' says the letters should be written backwards (in a down clue, letters climb up).
'nawor' can be found hidden inside 'complain a workmans'.
'nawor' backwards is 'ROWAN'.
(Other definitions for rowan that I've seen before include "ash native to mountain regions" , "Tree - archbishop" , "Mountain-ash" , "Sort of ash" , "The mountain ash tree" .)