Law officer providing wise men with unusual treats (10)
I believe the answer is:
magistrate
'law officer' is the definition.
'wise men with unusual treats' is the wordplay.
'wise men' becomes 'magi' (the three wise men from the nativity).
'with' is a charade indicator (letters next to each other).
'unusual' indicates an anagram.
'treats' anagrammed gives 'strate'.
'magi'+'strate'='MAGISTRATE'
'providing' is the link.
(Other definitions for magistrate that I've seen before include "Person in court" , "your worship" , "Court officer" , "Court head" , "Court official" .)