Some could help a man to climb a tree (5)
I believe the answer is:
maple
'a tree' is the definition.
(maple is a kind of tree)
'some could help a man to climb' is the wordplay.
'some' indicates a hidden word (some parts of the word are used).
'to climb' shows that the letters should be reversed in order (I've seen 'climbing' mean this (in a down clue, letters climb up)).
'elpam' is hidden in the letters of 'could help a man'.
'elpam' backwards is 'MAPLE'.
(Other definitions for maple that I've seen before include "Tree providing syrup" , "Its leaf is the emblem of 8 down" , "Tree; sauce" , "Tree with winged seeds" , "Hard light-coloured wood used for furniture" .)