using System;

using System.Reflection;

using System.Collections.Generic;

using System.Linq;

using System.Linq.Expressions;

public class Program

{

    public static void Main()

    {

        object item = new Teste();

        Console.WriteLine("Hello World");

        Console.WriteLine("1");

        var firstItem = ((IEnumerable<object>)item.GetType().GetProperties().First().GetValue(item)).First();

        var listType = typeof(List<>).MakeGenericType(firstItem.GetType());

        var lista = (IEnumerable<object>)Activator.CreateInstance(listType);

        listType.GetMethod("Add").Invoke(lista, new []{ firstItem });

        item.GetType().GetProperties().First().SetValue(item, lista);

    }

    public class Teste

    {

        public ICollection<Teste2> t2 { get; set; } = new List<Teste2>() { new() };

    }

    public class Teste2

    {

        public int t3 { get; set; } = 0;

    }

    public class Teste3

    {

    }

}