silver-bell tree vs silver bell

silver-bell tree and silver bell both are nouns.

Word	Noun	Adjective	Verb	Adverb
silver-bell tree	Yes	No	No	No
silver bell	Yes	No	No	No

As nouns, silver bell is a hypernym of silver-bell tree; that is, silver bell is a word with a broader meaning than silver-bell tree:

silver-bell tree: medium-sized tree of West Virginia to Florida and Texas
silver bell: any of various deciduous trees of the genus Halesia having white bell-shaped flowers

silver-bell tree (noun)	silver bell (noun)
medium-sized tree of West Virginia to Florida and Texas	any of various deciduous trees of the genus Halesia having white bell-shaped flowers