Trees in locations bisected by motorway (5)
I believe the answer is:
limes
'trees' is the definition.
(lime is a kind of tree)
'locations bisected by motorway' is the wordplay.
'locations' becomes 'lies' (lie is a kind of location).
'bisected by' is an insertion indicator (inserted letters split or bisect other letters).
'motorway' becomes 'M' (as in motorway names - Ml, Ms etc).
'lies' enclosing 'm' is 'LIMES'.
'in' acts as a link.
(Other definitions for limes that I've seen before include "Green fruit" , "Citrus fruit" , "Citrus trees" , "Pieces of fruit" , "Citrus fruits" .)