treatise vs written material

treatise and written material both are nouns.

Word	Noun	Adjective	Verb	Adverb
treatise	Yes	No	No	No
written material	Yes	No	No	No

As nouns, written material is a hypernym of treatise; that is, written material is a word with a broader meaning than treatise:

treatise: a formal exposition
written material: the work of a writer; anything expressed in letters of the alphabet (especially when considered from the point of view of style and effect)

Other hypernyms of treatise include piece of writing, writing.

treatise (noun)	written material (noun)
a formal exposition	the work of a writer; anything expressed in letters of the alphabet (especially when considered from the point of view of style and effect)