holm oak vs oak tree

holm oak and oak tree both are nouns.

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

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

holm oak: evergreen oak of southern Europe having leaves somewhat resembling those of holly; yields a hard wood
oak tree: a deciduous tree of the genus Quercus; has acorns and lobed leaves

Other hypernyms of holm oak include oak.

holm oak (noun)	oak tree (noun)
evergreen oak of southern Europe having leaves somewhat resembling those of holly; yields a hard wood	a deciduous tree of the genus Quercus; has acorns and lobed leaves
hard wood of the holm oak tree