Dressed trees round area for festival (6)
I believe the answer is:
easter
'festival' is the definition.
(I've seen this before)
'dressed trees round area' is the wordplay.
'dressed' indicates anagramming the letters ('dress' can mean 'prepare').
'round' is an insertion indicator.
'area' becomes 'a' (maths abbreviation).
'trees' is an anagram of 'ester'.
'ester' going around 'a' is 'EASTER'.
'for' acts as a link.
(Other definitions for easter that I've seen before include "Christian celebration of the Resurrection" , "Annual religious festival" , "Church festival" , "Resurrection festival" , "Christian festival in Spring" .)