If it were a different point in American history, he would have been executed for disregarding his duty to President Trump and pledging his help to Xi Jinping.
Except he did nothing of the sort.
Unless Trump was actually planning to nuke China.
SO let's review what happened here. Trump went around talking a lot of smack about China, which lead to some legitimate concerns by the Chinese that the US Might attack China. When Chinese officials raised these concerns to Milley during meetings, Milley assured them that Trump had no such intention.
It would have been nice to have a president who wasn't such a crazy actor that this was a legitimate concern the Chinese had.