A large tree from the mountains (6)
I believe the answer is:
alpine
'from the mountains' is the definition.
'a large tree' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'tree' becomes 'pine' (pine is a kind of tree).
'a'+'l'+'pine'='ALPINE'
(Other definitions for alpine that I've seen before include "Relating to high mountains" , "To do with great European mountains" , "Nepali (anag.)" , "Plant of high mountains" , "from Germany, Austria etc" .)