Tree half hidden on one side of Berlin (6)
I believe the answer is:
linden
'tree' is the definition.
(linden tree is a kind of tree)
'half hidden on one side of berlin' is the wordplay.
'half' suggests halving the letters.
'on' means one lot of letters go next to another.
'one side of' means to take half the letters.
'hidden' halved is 'den'.
'berlin' halved is 'lin'.
'den' put after 'lin' is 'LINDEN'.
(Other definitions for linden that I've seen before include "Lime tree" , "Tree with Lea - also called 8" , "One twigged" , "Unter den ------, iconic boulevard in Berlin" , "type of tree" .)