It was a compromise to appease both sides of the debate. They decided to have a bicameral legislature in order to encompass both systems. One that has equal representation regardless of the size of the state, and one system that has representation based on the number of the population. This way both sides would be happy, and that's why today there is the Senate and the House of Representatives, and both houses form the Congress which is the seat of federal power.
Treason is the only crime specifically defined in the Constitution. According to Article III, Section 3, a person is guilty of treason if he or she goes to war against the United States or gives “aid or comfort” to an enemy. So in short words, treason.