As for treason, that requires an "enemy" (foreign or domestic) to whom "aid and comfort" are provided. There has never been any official definition which provides a comprehensive test of who would qualify as an "enemy," although a nation with whom the US is officially at war (by Congressional declaration) would certainly qualify. Ultimately, that's a political question. If Russia is an enemy, then there are many joint programs and exchanges going on between the US and Russia that would qualify as treason.
The Supreme Court has already answered the question of whether it's legal to receive information which was obtained illegally by someone else. You can find out their answer by reading about the Pentagon Papers. I'll leave that as an exercise for the audience.
For Democrats and their captive media, the evidence doesn’t matter. Its the seriousness of the charge.
And the charge is “Russian Collusion.”