oval kumquat vs kumquat tree

oval kumquat and kumquat tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
oval kumquat	Yes	No	No	No
kumquat tree	Yes	No	No	No

As nouns, kumquat tree is a hypernym of oval kumquat; that is, kumquat tree is a word with a broader meaning than oval kumquat:

oval kumquat: shrub bearing oval-fruited kumquats
kumquat tree: any of several trees or shrubs of the genus Fortunella bearing small orange-colored edible fruits with thick sweet-flavored skin and sour pulp

Other hypernyms of oval kumquat include cumquat, kumquat.

oval kumquat (noun)	kumquat tree (noun)
shrub bearing oval-fruited kumquats	any of several trees or shrubs of the genus Fortunella bearing small orange-colored edible fruits with thick sweet-flavored skin and sour pulp