Cap on British tree cultivation (5)
I believe the answer is:
beret
'cap' is the definition.
(beret is a kind of cap)
'british tree cultivation' is the wordplay.
I cannot really understand how this works, but
'british' could be 'b' (abbreviation e.g. in BBC) and 'b' is present in the answer.
an anagram of 'tree' is 'eret' which is within the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'on' acts as a link.
Can you help me to learn more?
(Other definitions for beret that I've seen before include "Round flattish cap" , "Part of kit" , "French-style cap" , "Basque headgear" , "Military cap" .)