Treat is playing The Entertainer (7)
I believe the answer is:
artiste
'the entertainer' is the definition.
(artiste is a kind of entertainer)
'treat is playing' is the wordplay.
'playing' indicates anagramming the letters.
'treat'+'is'='treatis'
'treatis' anagrammed gives 'ARTISTE'.
(Other definitions for artiste that I've seen before include "Performers" , "Professional performer" , "Trouper" , "Attires like entertainer" , "A sitter for creative person" .)