Vertical alignments can be created using different methods, the below code shows profile creation using 2 points on existing horizontal alignment.

Example

internal bool CreateVerticalAlignment(Alignment alignment)
        {
            //ConsensusConnectionEdit allows the persistence of civil objects to the dgn
            Bentley.CifNET.SDK.Edit.ConsensusConnectionEdit con = Bentley.CifNET.SDK.Edit.ConsensusConnectionEdit.GetActive();

            //Define 2 points here for profile geometry creation assuming Slope = 10
            Bentley.GeometryNET.DPoint3d point1 = new Bentley.GeometryNET.DPoint3d(0, 50);
            Bentley.GeometryNET.DPoint3d point2 = new Bentley.GeometryNET.DPoint3d(800, 60);

            //Create geometry ProfileLine from 2 points 
            Bentley.CifNET.LinearGeometry.ProfileLine profileLine = new Bentley.CifNET.LinearGeometry.ProfileLine(point1, point2);
            if (profileLine == null) return false; 
            
            //create profile 
            Bentley.CifNET.GeometryModel.SDK.Profile profile = alignment.CreateProfileByProfileElement(profileLine, true, false);
            if (profile == null) return false;

            //Set feature definition to profile
            profile.SetFeatureDefinition("Alignment\\Geom_Baseline", "ProfileLondonRd");
            
            return true;
        }

CreateProfileByProfileElement() is used here to create profile on existing alignment named as "alignment". ProfileLine is passed as an argument to this function which is created using 2 points.