Puma, say, mountain animal originally seen in tree (7)
I believe the answer is:
catalpa
'tree' is the definition.
(catalpa is a kind of tree)
'puma say mountain animal originally' is the wordplay.
'puma say' becomes 'cat' (puma is a kind of cat).
'mountain' becomes 'alp' (alp is a kind of mountain**).
'originally' suggests taking the first letters.
The initial letter of 'animal' is 'a'.
'cat'+'alp'+'a'='CATALPA'
'seen in' acts as a link.
(Other definitions for catalpa that I've seen before include "Tree with heart-shaped leaves" , "it blossoms" , "A pal cat found in the American tree" .)