Tree has nuts (3)
I believe the answer is:
ash
'tree' is the definition.
(ash tree is a kind of tree)
'has nuts' is the wordplay.
'nuts' is an anagram indicator (nuts can mean crazy).
'has' is an anagram of 'ASH'.
(Other definitions for ash that I've seen before include "Silvery grey" , "Tree with keys" , "Tree; fire residue" , "Tree - effect of burning" , "Wooden" .)