expansion vs expanding upon

expansion and expanding upon both are nouns.

Word	Noun	Adjective	Verb	Adverb
expansion	Yes	No	No	No
expanding upon	Yes	No	No	No

As nouns, expansion and expanding upon are synonyms defined as:

expansion (noun)	expanding upon (noun)
the act of increasing (something) in size or volume or quantity or scope	adding information or detail
adding information or detail
a discussion that provides additional information
a function expressed as a sum or product of terms