Why does ivan confess to treason?

Shukhov had been sentenced for high treason after confessing to surrendering to the Germans with the intention of betraying his country and returning from captivity to carry out a mission for the Germans. In reality, in 1942, when the entire army was surrounded on the Western front, Shukhov was part of a group rounded up in the forest by the Germans. After a day or two in captivity, he and four other men escaped and made their way through the forest back to their own army. Two were shot on the spot by a machine gunner and a third died from his wounds. Though Shukhov and the other surviving escapee told the truth, that they were escaped POWs, they were accused of concocting a cover story.