None. Abraham Lincoln refused to allow it.
Merryman was a citizen of Maryland. Maryland did not secede. He actively aided the enemies of the United States.
He could easily have been hanged based on the standards used to hang loyal Texans in Gainesville, Texas in 1862. In that instance --I just read this recently-- confessions were elicited from slaves -- every slave in the county was whipped according to the one source. And, the "court" stipulated that the convictions could be obtained by a majority vote by the jury. And the majority of the jury members were slave holders.
Forty loyal Texans were hanged even though no overt acts were proved on any of them.
Merryman was released after 49 days in jail.
Walt
There were 60-odd confederate leaders who were indicted for treason or related charges. They were never tried because in the view of the Chief Justice of the Supreme Court, Salmon Chase, the passage of the 14th Amendment provided punishment for those who supported the rebellion. Trying and convicting them again on treason charges would have violated their 5th Amendment protections against double jeopardy. Absent the 14th Amendment, Jefferson Davis and dozens of others might have spent their remaining years in a jail cell.