high treason
From Longman Dictionary of Contemporary Englishhigh treasonˌhigh ˈtreason noun [uncountable] SCLPthe crime of putting your country in great danger, for example by giving military secrets to the enemyExamples from the Corpushigh treason• Stone was arrested on a charge of high treason on 3 May 1794 and was taken to the Tower of London.• Probably to the relief of the nationalists, he stood convicted of high treason at last.