Writer skirts around tree (5)
I believe the answer is:
pecan
'tree' is the definition.
(pecan is a kind of tree)
'writer skirts around' is the wordplay.
'writer' becomes 'pen' (something which writes).
'skirts' indicates putting letters inside (skirt can mean to go around).
'around' becomes 'ca' (circa).
'pen' placed around 'ca' is 'PECAN'.
(Other definitions for pecan that I've seen before include "Smooth pinkish-brown nut, nice in pie" , "Nut with sweet oily kernel" , "Pinkish-brown nut used in American pie" , "of nuts" , "US nut tree" .)