How to get selected values in an ASP MVC ListBox?

Greetings, I have a problem with my code in Asp Mvc 5, I have several related models and I have a Listbox that filters the values of a foreign key, but when I try to save it, only a single value is saved, not all the selected ones, and that ultimoes what I need.

This is my code, The Student.cs class

 public class Estudiante
{

   public int EstudianteId { get; set; }

    [Required]
    [Display(Name = "Nombre")]
   public string nombre {  get; set; }


  public virtual int MateriaId { get; set; }

    public virtual Materia Materia { get; set; }

}

The class Materia, Materia.cs

 public class Materia
{

   public int MateriaId { get; set; }

    [Required]
    [Display(Name ="Asignatura")]
   public string asignatura {  get; set; }



    public virtual ICollection<Estudiante> Estudiantes { get; set; }
    public virtual int ProfesorId { get; set; }
    public virtual Profesor Profesor { get; set; }


}

the Professor.cs class,

 public class Profesor
{

 public int ProfesorId { get; set; }
    [Required]

    [Display(Name="Profesor")]
    public string name { get; set; }

    public virtual ICollection<Materia> Materias { get; set; }


}

And the listbox in the Create, Create.cshtml action.

<div class="form-group">
        @Html.LabelFor(model => model.MateriaId, "Materias", htmlAttributes:     new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.ListBox("MateriaId",ViewBag.MateriaId as MultiSelectList,new { Multiple="multiple", size = "10"})
            @Html.ValidationMessageFor(model => model.MateriaId, "", new { @class = "text-danger" })
        </div>
    </div>

in the driver, StudentsController.cs

[HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Create([Bind(Include = "EstudianteId,matricula,nombre,apellido,fecha,MateriaId")] Estudiante estudiante)
    {
        if (ModelState.IsValid)
        {
            db.Estudiantes.Add(estudiante);
            db.SaveChanges();
            return RedirectToAction("Index");
        }
        //get profesor name



        ViewBag.MateriaId = new SelectList(db.Materias, "MateriaId", "asignatura", estudiante.MateriaId);

        return View(estudiante);
    }

and in the index

public ActionResult Index()
    {
        var estudiantes = db.Estudiantes.Include(e => e.Materia).Distinct().ToList();



        return View(estudiantes.ToList());
    }

What I need is for the listbox to save all the elements instead of just one. Thanks in advance.