General Milley secretly worked with the enemy, promising to notify them of any upcoming attack.
The American State, by which I mean the permanent structures of political power at the federal level in this country (as opposed to the government---i.e., the elected, appointed and bureaucratic personnel who move into and out of the State structures) is weakening. Lines of authority rest ultimately on faith in the legitimacy of such authority, and we've seen numerous examples of actors within the government attempting to subvert constitutional authority. Recent revelations about Milley evoke older stories of Peter Strzok, Lisa Page, James Comey and likely others whose names I've forgotten. As the legitimacy of constitutional order fails and compliance with legal authority ceases to be observed, the continued existence of the State itself is open to question. While history doesn't always precisely repeat, look again at the example of Russia in 1917. The Tsar was not overthrown by the Bolsheviks---his authority, for numerous reasons, crumbled beneath him.
Final point: this allegation comes not from Milley, China, or Trump directly but Woodward's book indirectly.
As such, if you are to believe what Woodward says about Milley in the book is true then you should believe everything else Woodward says about Trump in the same book is true.
But we aren't going to do that, right?
Whoever, owing allegiance to the United States, levies war against them or adheres to their enemies, giving them aid and comfort within the United States or elsewhere, is guilty of treason and shall suffer death
Minor problem with the calls for treason: China is neither an enemy of the USA nor engaged in a war with her.
Hence giving them aid or comfort... in this case warning them that Trump might be unhinged enough to fire a nuke at them... is not treason.
It's likely that there are many in the military that are secretly working with China, and we need to smoke them out. We need congressional hearings and subpoenas. We need an independent council.
In the hierarchy war secrets, an attack is in the highest tier of secrecy.
By warning China of an attack, the consequence is that American soldiers will die. Their deaths is Milley's responsibility.
We have a smoking gun!