Flower, say, in say, seasonal treat (6,3)
I believe the answer is:
easter egg
'seasonal treat' is the definition.
(I've seen this before)
'flower say in say' is the wordplay.
'flower' becomes 'aster' (type of flower).
'say' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'in' means one lot of letters goes inside another.
'say' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'aster'+'eg'='astereg'
'astereg' going inside 'eg' is 'EASTER EGG'.
(Other definitions for easter egg that I've seen before include "festival food" , "Programmer's surprise" , "Segregate from traditional chocolate ovum" , "Seasonal fare" , "Seasonal gift" .)