Добавить элементы в словарь - C#

KeyValuePair

category

probability

 private class ParcelProbability
        {
            public readonly Dictionary<double, KeyValuePair<int,double>> ParcelProb = new Dictionary<double, KeyValuePair<int,double>>();
 
            public void FillIn(double parcelid, int category, double probability)
            {
                ParcelProb.Add(parcelid /*how to add category, probability to KeyValuePair?*/ );
            }
        }