There was no one to treat with. As President Lincoln said, no one man could give up the rebellion for another.
In law, the so-called CSA had no more validity than the "outhouse republic" in Texas a few years back. In fact, the outhouse republic maintained its territorial integrity longer than the so-called CSA did.
Walt
Yes there was. Southerners attempted repeatedly to secure a meeting with Lincoln between January and Fort Sumter. He refused EVERY SINGLE ONE of them. That included not only envoys from Davis and the confederate states but high ranking leaders from the states themselves. Among those who attempted to meet with Lincoln were the Attorney General of South Carolina, Congressman Martin Crawford of Georgia, and former Governer Andre Roman of Louisiana. Lincoln refused every single one of them. He also refused calls for meetings with the south to be hosted by at least two sitting US Senators who had not seceded yet - Robert M.T. Hunter and Louis T. Wigfall. He would not meet with any of the southerners, be it formally or informally, be they an official or simply an envoy, or even be it through an intermediary in the senate.
The simple fact is that Lincoln did not want diplomacy. He did not want to compromise. He did not want to settle the matter in any way other than either complete subservience to his demands or a meeting on the battlefield.