As I understand the Constitution, Milley would have had to have actually called in order to come anywhere near committing treason. Further, Congress had not declared war on China.
Treason against the United States, shall consist only in levying War against them, or in adhering to their Enemies, giving them Aid and Comfort. 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.
[The Congress shall have Power . . . ] To declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water; . . .