Tree with less on top? Not initially (5)
I believe the answer is:
'tree' is the definition.
(alder is a kind of tree)
'less on top? not initially' is the wordplay.
'less on top?' becomes 'balder' (I've seen this before).
'not initially' means to remove the first letter.
'balder' with its first letter removed is 'ALDER'.
'with' acts as a link.
(Other definitions for alder that I've seen before include "Birch relative" , "Tree or shrub whose wood is resistant to underwater rot" , "Shrub or tree with cone-like fruits" , "One [TYPE OF TREE]" , "Forward movement" .)