Flat surface for tree (5)
I believe the answer is:
plane
I believe this is a double definition.
'flat surface' is the first definition.
(I've seen this in another clue)
'tree' is the second definition.
(plane is a type of tree)
'for' acts as a link.
(Other definitions for plane that I've seen before include "Woodworking tool" , "What imitates bird" , "Tree - figure - aircraft" , "Flat surface; tree" , "that soars into the sky" .)