Light work, shaking a tree-top (8)
I believe the answer is:
operetta
'light work' is the definition.
(I've seen this before)
'shaking a tree-top' is the wordplay.
'shaking' indicates anagramming the letters.
'a'+'tree'+'top'='atreetop'
'atreetop' anagrammed gives 'OPERETTA'.
(Other definitions for operetta that I've seen before include "Patience perhaps" , "Short amusing opera" , "Light musical drama" , "Light musical theatre" , "light-hearted performance" .)