Tree in middle is removed (6)
I believe the answer is:
poplar
'tree' is the definition.
(poplar is a kind of tree)
'in middle is removed' is the wordplay.
'in' becomes 'popular' (I've seen this before).
'middle is removed' suggests removing the centre.
'popular' with its centre taken out is 'POPLAR'.
(Other definitions for poplar that I've seen before include "The tree that quivers" , "Tree, maybe from Lombardy" , "Tall, slender tree" , "Tall fast-growing tree; East London area" , "The tree is almost liked" .)