Oh come on. Treason? That's a little extreme. I was very upset with their decision, but I don't believe they committed treason.
There is a separation of powers in this country. Supreme Court justices will use their powers as they see fit. If you don't like how they are using their powers then vote for a President who will appoint someone you like.
If the House and Senate thinks an individual justice should be impeached then they have the power to impeach that justice. Samuel Chase was impeached by the House in 1804, but was acquitted by the Senate. He's the only justice to have been impeached in our history.