sweet orange vs sweet orange tree

sweet orange and sweet orange tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
sweet orange	Yes	No	No	No
sweet orange tree	Yes	No	No	No

As nouns, sweet orange and sweet orange tree are synonyms defined as:

sweet orange and sweet orange tree: probably native to southern China; widely cultivated as source of table and juice oranges

Other synonyms of sweet orange include Citrus sinensis.

sweet orange (noun)	sweet orange tree (noun)
orange with sweet juicy pulp; often has a thin skin	probably native to southern China; widely cultivated as source of table and juice oranges
probably native to southern China; widely cultivated as source of table and juice oranges