Tree of metal and sand, say (6,5)
I believe the answer is:
copper beech
'tree' is the definition.
(copper beech is a kind of tree)
'metal and sand say' is the wordplay.
'metal' becomes 'copper' (copper is a kind of metal).
'and' says to put letters next to each other.
'sand' becomes 'beach' (sand can refer to a sandy beach).
'say' indicates a 'sounds like' (homophone) clue.
'beach' sounds like 'beech'.
'copper'+'beech'='COPPER BEECH'
'of' acts as a link.
(Other definitions for copper beech that I've seen before include "Tree with dark leaves" , "Never-green tree" , "Leaving body" , "Tree with purplish-brown leaves" , "Purplish-leaved tree" .)