Willow tree somehow rose around one (5)
I believe the answer is:
osier
'willow tree' is the definition.
(osier is a kind of willow tree)
'somehow rose around one' is the wordplay.
'somehow' indicates anagramming the letters.
'around' indicates putting letters inside.
'one' becomes 'i' (roman numeral).
'rose' with letters rearranged gives 'oser'.
'oser' going around 'i' is 'OSIER'.
(Other definitions for osier that I've seen before include "Basket-making material" , "growing in a bed" , "Tree for basket making" , "Basket material" , "Small willow; its shoot" .)