Charlie Martin over at PJMedia notes the actual Constitutional definition:
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....Article III, Section 3, clause 1. And why is it defined so narrowly? As Charlie points out, it's because where we (the inhabitants of the colonies, that is) came from, "treason" was whatever the King or Queen didn't like. Rather than continue to subject ourselves to the pique of an individual, the Founders (who would certainly have been tried as traitors if they'd lost the war) decided to make it very clear that criticism of the government, the president, the flag, apple pie, motherhood, or those who choose not to undertake motherhood is not treason.
Enough with the hysterics, Democrats - neither the President nor members of his cabinet have committed treason. And Republicans, reporters aren't committing treason by being unabashedly biased and hostile toward the President, either.