That would be a different crime. Espionage.

The Rosenbergs who gave Atomic Secrets to the Soviets were not tried for treason, but for espionage, because we were not in a declared war with the USSR.

Also it was held in a regular federal court, not a military tribunal.

It's still a serious crime.

Sentencing and Penalties for Espionage

Sentences and other penalties for espionage vary according to the facts of the case, but typically include long prison sentences, often for life (as do other crimes against the government). Members of the military who are convicted of the crime may receive the death penalty "or such other punishment as a court-martial may direct," according the the Uniform Code of Military Justice. While most federal crimes have a five-year statute of limitations, acts of espionage generally carry a 10-year statute of limitations.