big tree vs Sequoia Wellingtonia

big tree and Sequoia Wellingtonia both are nouns.

Word	Noun	Adjective	Verb	Adverb
big tree	Yes	No	No	No
Sequoia Wellingtonia	Yes	No	No	No

As nouns, big tree and Sequoia Wellingtonia are synonyms defined as:

big tree and Sequoia Wellingtonia: extremely lofty evergreen of southern end of western foothills of Sierra Nevada in California; largest living organism

Other synonyms of big tree include giant sequoia, Sequoia gigantea, Sequoiadendron giganteum, Sierra redwood.

big tree (noun)	Sequoia Wellingtonia (noun)
extremely lofty evergreen of southern end of western foothills of Sierra Nevada in California; largest living organism	extremely lofty evergreen of southern end of western foothills of Sierra Nevada in California; largest living organism