The Constitution of the United States includes, in Article III, Section 3, on treason:
No Person shall be convicted of Treason unless on the Testimony of two Witnesses to the same overt Act, or on Confession in open Court.
Constitutional proof of treason, consistent with the aforesaid, exists in the following document:
That copy is from the website of the Pasco Clerk & Comptroller (Online Court Records Search) where it is entered under the title MEMORANDUM AND MOTIONS.