Discuss about one tree (7)
I believe the answer is:
conifer
'tree' is the definition.
(conifer is a kind of tree)
'discuss about one' is the wordplay.
'discuss' becomes 'confer' (conferring is a kind of discussing).
'about' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'confer' going around 'i' is 'CONIFER'.
(Other definitions for conifer that I've seen before include "In force (anag.)" , "The tree keeps its leaves" , "one branching out" , "Evergreen tree" , "Eg, pine, fir or cypress" .)