https://www.congress.gov/bill/116th-congress/senate-bill/488/text [KH, KB]
18 USC Ch. 115: TREASON, SEDITION, AND SUBVERSIVE ACTIVITIES:
http://uscode.house.gov/view.xhtml?path=/prelim@title18/part1/chapter115&edition=prelim
Punishment for treason is "death" or imprisonment. USC doesn't specify the manner of death.
So, the real question is: why would they think that the penalty for treason or sedition would be hanging?