When you create a new group, you can make it operate in or versioned or unversioned mode (I am using the 'mode' term very losely here). In the case of DMSample, we have no group set up to operate in unversioned mode, with the consequence being that the drop-down does not give you any group. I suspect the same is happening in your application.
My first reply is centered around the technical clarification. To the point of best practices and future-proof implementations, using proposition data (aka, unversioned propositions) is not recommended, you should use decision data (aka, versioned propositions) .
Aniket, what is that you are trying to achieve by using unversioned propositions as opposed to decision data?
Basically if a service/product offered to customer can change its characteristics (availability, cost etc.), then whether it should be created as proposition (decision data) or should it be created as a data set (like normal Data classes inherited from Data-).