He's clinging to top of pear tree (5)
I believe the answer is:
maple
'tree' is the definition.
(maple is a kind of tree)
'he's clinging to top of pear' is the wordplay.
'he' becomes 'male' (I've seen this in other clues).
'clinging to' means one lot of letters goes inside another.
'top of' indicates taking the first letters.
The initial letter of 'pear' is 'p'.
'male' enclosing 'p' is 'MAPLE'.
(Other definitions for maple that I've seen before include "Tree providing syrup" , "Tree producing syrup" , "Syrup-yielding tree" , "Canadian flag leaf" , "Tree with winged seeds" .)