using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Dictionary<Type, List<A>> dict = new();

        A foo = new A();

        A bar = new B();

        dict.Add(foo.GetType(), new List<A>());

        dict.Add(bar.GetType(), new List<A>());

        dict[foo.GetType()].Add(foo);

        dict[bar.GetType()].Add(bar);

        foreach (var a in dict[foo.GetType()])

        {

                Console.WriteLine(a.ToString());

        }

    }

}

class A{

public override string ToString(){return "a";}

}

class B : A{

public override string ToString(){return "b";}

}