Are we fighting a war with China?
From Wikipedia:
Oran's Dictionary of the Law (1983) defines treason as "...[a]...citizen's actions to help a foreign government overthrow, make war against, or seriously injure the [parent nation]." In many nations, it is also often considered treason to attempt or conspire to overthrow the government, even if no foreign country is aiding or involved by such an endeavor.
The point is, if we can argue about it, then there should be a fair trial to determine whether or not it was treason. The president and other leaders saying it's treason doesn't lend itself to a fair trial in the future. The appropriate response is "He committed crimes, we will have a trial to determine the extent of those crimes and whether or not it is treason".
And who do you think will carry out these killings?
(Hopefully you have a credible source to back up your claims...)