IIRC from my history lessons, Texas has one potential way of removing itself form the Union within the context of the Contract it signed when joining the Union. Texas has the legal right to split itself into 5 separate States at any time. This would give Texas 10 Senators, and 10? more Congressmen and the extra Electoral College votes as well.
Should Texas decide to do that, it would virtually take over the Federal Govt. Given that this would be an unpopular move then there is a real chance that the Union would fight against it. That would create a breach of contract and Texas would regain it's status as an independent Republic.
As an independent Republic, Texas would be one of the wealthiest nations in the world, having the 8th largest economy in the world today; and would be quite capable of sustaining itself, and enjoying a prosperous future, without having the likes of California or Louisana clinging onto it's back.
Treason? Not even close.
‘‘Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest.’’ ~ Mahatma Ghandi, "Gandhi, An Autobiography", page 446
‘‘The great object is that every man be armed. Everyone who is able may have a gun.’’ ~ Patrick Henry