Bloke protects core of apple tree (5)
I believe the answer is:
maple
'tree' is the definition.
(maple is a kind of tree)
'bloke protects core of apple' is the wordplay.
'bloke' becomes 'male' ().
'protects' indicates putting letters inside.
'core of' says to take the centre.
The central letter of 'apple' is 'p'.
'male' placed around 'p' is 'MAPLE'.
(Other definitions for maple that I've seen before include "Ample (anag.)" , "----- leaf: symbol of Canada" , "Tree yielding syrup" , "Syrup-yielding tree" , "Tree; sauce" .)