Talk together about single evergreen tree (7)
I believe the answer is:
conifer
'evergreen tree' is the definition.
(I've seen this before)
'talk together about single' is the wordplay.
'talk together' becomes 'confer' (I've seen this before).
'about' means one lot of letters goes inside another.
'single' becomes 'i' (one).
'confer' placed around 'i' is 'CONIFER'.
(Other definitions for conifer that I've seen before include "Eg, pine, fir or cypress" , "one branching out" , "Fir or pine, for example" , "Type of tree" , "The tree keeps its leaves" .)