using System;

using System.Linq;

using System.Collections.Generic;

using System.Collections;

using System.Threading;

using System.Threading.Tasks;

using System.Net;

using System.Diagnostics;

​

public class Program

{

    public static void Main()

    {

        var program = new Program();

        var items = new List<I> { new A(), new A(), new B() };

        var groups = items.GroupBy(x => x.GetType());

​

        foreach(var g in groups)

        {

​

            var dataItemType = g.Key;

            var listType = typeof(List<>).MakeGenericType(new [] { dataItemType });

            var list = (IList) Activator.CreateInstance(listType);

            foreach(var data in g)

                list.Add(data);

​

            program.GetType()

                   .GetMethod("InsertBulk")

                   .MakeGenericMethod(dataItemType)

                   .Invoke(program, new object[] { list });

​

        }

    }

    public void InsertBulk<T>(IEnumerable<T> ts) {

        Console.WriteLine(typeof(T).FullName);

        Console.WriteLine(ts.Count());

    }

}

​

public class I {}

public class A : I {}

public class B : I {}