List of checkboxes

Hi,

In my database I have Offers, Levels(basic, intermediate, expert) and OfferLevels tables. One offer can have zero or multiple Levels.

I can create website which will create new offer but I cant figure out how to write levels to OfferLevels table.

I want to display levels as 3 checkboxes.

Could somebody help me with how to write controller, viewmodel(hold offer and levels objects) and view with asp.net core?

My code:

Controller
        public IActionResult Create()
        {
            var viewModel = new ViewModel();
            return View(viewModel);
        }

        [HttpPost]
        [ValidateAntiForgeryToken]
        public IActionResult Create(ViewModel viewModel)
        {
            if (ModelState.IsValid)
            {
                viewModel.Offer.OfferDate = DateTime.Now.ToLocalTime();
                context.Offers.Add(viewModel.Offer);
                context.SaveChanges();
                return RedirectToAction("Index");
            }

            return View(viewModel.Offer);
        }

ViewModel
    public partial class ViewModel
    {
        public Offer Offer { get; set; }
        public List<Level> Levels { get; set; }
    }

View
<form asp-controller="Home" asp-action="Create" method="post" class="form-horizontal" role="form"><div asp-validation-summary="All" class="text-danger"></div><div class="form-group"><label asp-for="Offer.OfferTitle"></label><input asp-for="Offer.OfferTitle" class="form-control" /><span asp-validation-for="Offer.OfferTitle" class="text-danger"></span></div>

....there should be checboxes dont how to put them here....

    <div class="form-group"><input type="submit" value="Create" class="btn btn-default" /></div></form>