Tree is more healthy with top removed (5)
I believe the answer is:
osier
'tree' is the definition.
(osier is a kind of tree)
'more healthy with top removed' is the wordplay.
'more healthy' becomes 'rosier' ('rosy' can be similar in meaning to 'healthy').
'with top removed' means to remove the first letter.
'rosier' with its first letter taken away is 'OSIER'.
'is' is the link.
(Other definitions for osier that I've seen before include "Willow for basket making" , "Flexible twig of a willow tree" , "growing in a bed" , "Basketry willow" , "Willow with twigs for basket-weaving" .)