American tree: ending of climb by absolute idiot (9)
I believe the answer is:
butternut
'ending of climb by absolute idiot' is the definition.
I can't tell whether this definition defines the answer.
'american tree' is the wordplay.
'american' becomes 'butter' (I can't explain this - if you can you should believe this answer much more).
'tree' becomes 'nut tree' (nut tree is a kind of tree).
'butter'+'nut'='BUTTERNUT'
Can you help me to learn more?
(Other definitions for butternut that I've seen before include "Wood" , "species of tree" , "Variety of pumpkin" , "sort of a squash" .)