chestnut oak vs oak tree

chestnut oak and oak tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
chestnut oak	Yes	No	No	No
oak tree	Yes	No	No	No

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

chestnut oak: an oak having leaves resembling those of chestnut trees
oak tree: a deciduous tree of the genus Quercus; has acorns and lobed leaves

Other hypernyms of chestnut oak include oak.

chestnut oak (noun)	oak tree (noun)
an oak having leaves resembling those of chestnut trees	a deciduous tree of the genus Quercus; has acorns and lobed leaves