You need a German minor win/cold peace in WW1. It would take a series of POD's.
1) Tsar is overthrown (OTL)
2) Germany makes a status quo, end the war peace offer in early 1917 (OTL). Russia accepts. (ATL).
3) German throws its FULL weight against France by September 1917, and is more successful. You likely need to slow the USA entering the war, so say no Zimmerman. In late 1918 or early 1919, a cold peace is made. Germany withdraws to 1914 Western border, loses colonies, blockade ends, no reparations.
4) Instead of going democratic, the White Russian government is fascist by 1925. For me, this is easy to see.
5) A very weak Germany still has economic turmoil, and the SDP end up in power, which over times turns into a communist government. It may not be Leninist, but it would fall withing the broad definition of Communism.
6) In the 1930's or 1940's Russia wants Poland, Lithuania back and WW2 starts.