The following is not the most likely course of events, in fact, is is rather far-fetched. But still:
During WWI, Russia is more successful, A-H less. Direct warfare between Germany and Russia is kept to the possible minimum.
Germany has less success overall. Avoiding the push through Belgium and just sitting in the forts of A-L is probably a wise tatctic, but might be seen as lack of any victories.
An earlier factual military dictatorship with the kaiser as figurehead leads to earlier and bigger discontent. Possibly there are very ill-advised repressive measures against the more and more critical SPD leadership before the SPD has time to split off Spartakusbund and USPD.
Having a cunning German Lenin-equivalent might help. The Deutsche Räterepublik is certainly farther to the Left than Weimar ever was.
Hm, look at the 1912 elections:
Interesting.
Maybe a revolutionary part in the middle, a strongly catholic part (backed by France?) in the West and South, with unrest in the Ruhr and Frankfurt areas and a separate Kingdom of (East) Prussia as a client kingdom, shielded from the rest by Russian soldiers in the newly acquired parts of Poland.
This would require that the dynasty and the conservative Junkers of East Prussia would see Tsarist Russia that beat them as less evil alternative compared to the Red Revolutionaries in Berlin. Seems possible.