These trees may be obtained from Wilhelmstrasse (4)
I believe the answer is:
elms
'these trees' is the definition.
(elm is a kind of tree)
'obtained from wilhelmstrasse' is the wordplay.
'obtained from' indicates the answer is hidden within the clue.
'ELMS' is hidden in the letters of 'wilhelmstrasse'.
'may be' acts as a link.
(Other definitions for elms that I've seen before include "may have many leaves" , "Mel's strange trees" , "Deciduous trees with rough serrated leaves" , "Trees sound like Cockney steering devices" , "Trees (of late, prone to disease)" .)