Storing object in Session

I know this subject has been treated in numerous posts but I just cannot work it out.

Within an Controller Inside an ActionResult I would like to store an object in the Session and retrieve it in another ActionResult. Like that :

    public ActionResult Step1()
    {
        return View();
    }

    [HttpPost]
    public ActionResult Step1(Step1VM step1)
    {
        if (ModelState.IsValid)
        {
            WizardProductVM wiz = new WizardProductVM();
            wiz.Step1 = step1;
            //Store the wizard in session
            // .....
            return View("Step2");
        }
        return View(step1);
    }

    [HttpPost]
    public ActionResult Step2(Step2VM step2)
    {
        if (ModelState.IsValid)
        {
            //Pull the wizard from the session
            // .....
            wiz.Step2 = step2;
            //Store the wizard in session again
            // .....
            return View("Step3");
        }
    }