A song about king caught hiding gold in tree (9)
I believe the answer is:
araucaria
'tree' is the definition.
(araucaria is a kind of tree)
'a song about king caught hiding gold' is the wordplay.
I cannot quite understand how this works, but
'a' is present in the answer.
'song' could be 'aria' (aria is a kind of song) and 'aria' is found in the answer.
'about' could be 'c' (abbreviation for 'circa') and 'c' is found within the answer.
'king' could be 'r' (r is abbreviation for rex) and 'r' is present in the answer.
'gold' could be 'au' (Au is the chemical symbol for gold) and 'au' is located in the answer.
No letters remain.
This may be the basis of clue (or it may be nonsense).
'in' is the link.
(Other definitions for araucaria that I've seen before include "Monkey puzzle tree (or Chile pine)" , "Coniferous tree" , "Monkey puzzle tree - Guardian cryptic crossword setter" , "puzzle for primates?" , "Evergreen" .)