Trunk with hollow rings within rings supporting treetop (5)
I believe the answer is:
torso
'trunk' is the definition.
('torso' can be a synonym of 'trunk')
'hollow rings within rings supporting treetop' is the wordplay.
'hollow' means to remove the middle letters.
'within' is an insertion indicator.
'rings' becomes 'oo' (multiple circles**).
'supporting' means one lot of letters go next to another (in a down clue, some letters go below others).
'treetop' becomes 't' (top of the word 'tree').
'rings' with its centre taken out is 'rs'.
'rs' put within 'oo' is 'orso'.
'orso' put after 't' is 'TORSO'.
'with' is the link.
(Other definitions for torso that I've seen before include "Poorly-dressed child" , "Roots out in trunk of the body" , "Roots (anag)" , "Body, minus its head and limbs" , "Chest" .)