Good one! Yes its explained pretty well here although explaining A "Trumped up" charge...

Others were accused of espionage and treason, but no one has been executed since 1942. Or course, the Rosenbergs is one of the most well-known cases of U.S. citizens executed, but they were not convicted of treason, for reasons explained below. Rather, they were executed for their conspiracy to commit espionage for the Soviet Union, transmitting information about the Manhattan project and other atomic bomb projects. The case is fascinating, as most legal scholars admit that they were guilty of espionage, but their case was full of judicial improprieties and therefore execution was probably inappropriate. They were executed in 1953. The last conviction of treason was in 1952.

The latest controversies concerning American citizens and acts of treason – aside from the Trump administration – are Edward Snowden and Chelsea Manning. Several Senators called Edward Snowden a traitor after releasing information about the NSA surveilling American citizens. However, the Constituion defines treason with specificity: “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 the Punishment of Treason, but no Attainder of Treason shall work Corruption of Blood, or Forfeiture except during the Life of the Person attainted.” Snowden did not levy war against the United States in the release of these documents (nor did Chelsea Manning). Providing ‘aid and comfort’ has limits – you must be aiding and abetting a country that the U.S. is actively engaged at war in. Similarly, that is why the Rosenbergs could not be charged with treason because, at the time, the United States was not at war with the Soviet Union. Espionage provisions typically are the gap-fillers for activities that appear treasonous when the U.S. is not at war.

https://www.theblanchlawfirm.com/a-history-of-treason-in-the-united-states/