A special apple finally grafted onto new tree (5)
I believe the answer is:
aspen
'tree' is the definition.
(aspen is a kind of tree)
'a special apple finally grafted onto new' is the wordplay.
'special' becomes 'sp' ().
'finally' says to take the final letters.
'grafted onto' means one lot of letters go next to another.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
The last letter of 'apple' is 'e'.
'a'+'sp'+'e'+'n'='ASPEN'
(Other definitions for aspen that I've seen before include "that's wooden" , "One trembling" , "winter resort" , "Colorado ski resort - tree" , "city in Colorado" .)