With something as touchy as treason, it would be wise to define treason in a very narrow way.
Mind you, that in the US 'Treason' is (essentially) defined soley as a citizen engaging in an act of war against the US.
The US definition of treason (defined in the US Constitution) is so narrow that I think only about 40 people have ever been charged with treason and even fewer convicted of it.
This is everyone I can find that was formally charged with threason in The United States (I could only find one actual conviction):
* Aldrich Ames, CIA, and his wife sold secrets to Soviets
* Benedict Arnold. Plotted to help Britain during the Revolutionary War.
* David Barnett, CIA, arrested 1980
* US Air Force Sergeant Herbert W. Boeckenhaupt sold secrets of Strategic Air Command to GRU
* Christopher Boyce, Andrew Daulton Lee arrested for selling secrets to Soviets
* Anthony Cramer
* Larry Wu-Tai Chin, CIA, spied for China for 3 decades
* Officials of the Confederacy, the most organized rebellion in the history of the U.S. Federal Government
* Iva Toguri D'Aquino, who is frequently identified with "Tokyo Rose".
* Velvalee Dickinson
* Governor Thomas Dorr 1844, convicted of treason against the state of Rhode Island; "Dorr Rebellion"
* Nelson C. Drummond, Navy, worked for GRU
* US Army Sergeant Jack Dunlap NSA courier, worked for GRU
* Iyman Faris, a former Ohio truck driver who was plotting with Al-Qaeda to destroy the Brooklyn Bridge.
* Ronald Grecula, on May 23, 2005, was arrested in the United States as an American citizen who was working with Al-Qaeda to build a bomb and deliver it to them.
* Robert Hanssen FBI counterintelligence agent, who sold top secrets to the Soviet Union for two decades
* Max Haupt
* Alger Hiss, State Department official, sold secrets to Soviet Union
* Tomoya Kawakita
* Tyler Kent, communications to Soviet Union, convicted 1941
* Fritz Kuhn, Nazi, held in internment camp, deported after world war II
* Edward Lee Howard, CIA, defected USSR 1985
* Timothy McVeigh, charged with the Oklahoma City Bombing, said to be the worst act of Domestic Terrorism in the United States.
* Ahmed F. Mehalba, a United States Air Force translator who was convicted of lying to government agents and removing classified documents from the Guantanamo Bay detention facility.
* Richard Miller FBI agent, arrested 1983
* Harold Nicholson CIA, arrested 1996
* Ronald W. Pelton NSA communications specialist, revealed to Soviets that US submarines tapped Soviet undersea cables
* William Perl spied for Soviet Union
* Jonathan Pollard US Naval Investigative Service, and wife Anna, spying for Israel
* Ezra Pound, brought back from Italy to face charge of treason for supporting Mussolini, declared insane and unfit to be tried
* The Saint Patrick's Battalion, Irish-Americans who fought for Mexico in the Mexican-American War.
* Earl Edwin Pitts, FBI, arrested 1996, secrets to Soviets
* Ethel and Julius Rosenberg, atomic bomb secrets to Soviet Union
* John Anthony Walker, a Soviet spy active during the Cold War; also some family members, Michael Anthony Walker
* John Walker Lindh, young Californian Muslim, joined the Afghani Taliban, although before September 11, 2001; accepted a plea bargain, 20 years in prison and a gag order lasting that long. He was not convicted of treason.
IOW, it's damned near impossible to convict someone of treason if treason consists only in the act of waging war against one's own country.