MVC C# Searc Filter : I'm trying to filter records from my database. Checkbox value post controller when checkbox checked,

I choose "a" and I show which  record contains "a", I choose "a,b" and I'm showing "a - b - a,b " but I want to show just "a,b"

My controller;

       public ActionResult GetProducts(List<string> filter)
        {
     List<Product> proc = new List<Product>();
            
            foreach (var item in filter )
             { 
                var model = db.Product.Where(x => x.tMal.Contains(item)).ToList();
             proc.AddRange(model);
             
              }
            return View(proc);


How Can I do?