It all depends on what you consider to be treason. There are many, myself included, who believe that there is no higher form of treason than for a politician to elevate himself above the Constitution. It was under Lincoln that this became possible marking the realization of Benjamin Franklin's warning about the Founders' bequest of a Republic "... if you can keep it."
But don't think me unfair to Lincoln or blind in my faith in the Founders. You can argue with some credibility that it was their failure to end slavery at the time of the founding that paved the way for Lincoln and his ilk to destroy the independence of the States a generation later. And the end of the sovereignty of the States was the end of limited government.
I'll buy that. My issue with most Lincoln-haters is their somewhat irrational assumption that if Lincoln hadn't resisted secession that somehow limited government would have survived in its pre-1860 form.
This seems highly unlikely to me. IOW, I believe those who attempted secession killed the pre-1860 Republic dead. Lincoln and Grant (and a couple million others) succeeded in resuscitating it to a limited extent.
The 1865 to 1900 Republic was also quite remarkably limited compared to the general and almost continuous trend since 1900 of increasing government power. It seems to me irrational to assume that this general trend would never have happened without Lincoln's precedent of expanding government power temporarily to deal with an existential crisis.