Again say thanks for putting in the new trees (7)
I believe the answer is:
restate
'again say' is the definition.
('state' can be a synonym for 'say' so perhaps 'restate' is OK for 'again say')
'thanks for putting in the new trees' is the wordplay.
'thanks for' becomes 'at' (I am not sure about this - if you are sure you should believe this answer much more).
'putting in' indicates putting letters inside.
'the new' indicates an anagram.
'trees' anagrammed gives 'reste'.
'at' put into 'reste' is 'RESTATE'.
Can you help me to learn more?
(Other definitions for restate that I've seen before include "Once more affirm" , "say, in other words" , "Go over" , "say, a different way" .)