Wilhelm sent for Lenin and shipped him to Russia to mess with the Monarchy. That internal disorder worked even better than Wilhelm had hoped, but it also had the effect of removing the threat from the East and letting him concentrate on the Western Front.
Correction: Lenin was sent to mess with the provisional government. The Tsar was out by then. The German involvement in Lenin’s return was intended to get the Russian army out of WWI.
The middle class party - Menshivics was struggling and Germany paid Lenin to go into Russia and set up a peace deal with Germany which was one way to get Russia out of World War One. The Tsar was long out of picture at that point. The Bolshevics were actually a small minority party at first.