public IEnumerable<Category> Get_category_list(int Id) 
        {
            return (from a in Category_table
                    where (a.ParentId == Id)
                    select new Category
                    {
                        Id = a.Id, 
                        NameCategory = a.NameCategory, 
                        DateCreateCategory = a.DateCreateCategory, 
                        ParentId = a.ParentId 
                    }).ToList();
        }

        public ActionResult List(int? Id)
        {
            int _id = Id ?? 0;
            Main_Linq_Aticles mla = new Main_Linq_Aticles();
            return View(mla.Get_category_list(_id));
        }

    <%foreach (var item in Model)
      { %>
      <%=item.NameCategory  %>
    ... ( и т. д )
    <%} %>

namespace WebApp.Controllers
{
    public class ProductsController : Controller
    {
        private I_Product_Repository i_pr_rep;
        public ProductsController( ) 
        {
            i_pr_rep = new Sql_product_repository();
        }
        public ViewResult List() 
        {
            //var pr = (from a in i_pr_rep.Products where a.Name == "Kayak" select new Product { Name = a.Name, Description = a.Description, Category = a.Category, Price = a.Price }).ToList();
            return View(i_pr_rep.Products.Where(a=>a.Name == "Kayak").ToList());
        }

    }
}

namespace WebApp.Models
{
    [Table(Name="Products")]
    public class Product
    {
        [Column(IsPrimaryKey=true,IsDbGenerated=true, AutoSync=AutoSync.OnInsert)]
        public int ProductId { get; set; }
        [Column]
        public string Name { get; set; }
        [Column]
        public string Description { get; set; }
        [Column]
        public decimal Price { get; set; }
        [Column]
        public string Category { get; set; }
    }
}

namespace WebApp.Models
{
    public interface I_Product_Repository
    {
        IQueryable<Product> Products { get; }
    }
}

namespace WebApp.Models
{
    public class Sql_product_repository : I_Product_Repository
    {
        private string string_to_connect = WebConfigurationManager.ConnectionStrings["Sql_base"].ConnectionString;
        private Table<Product> pr_table;
        public Sql_product_repository() 
        {  
            pr_table = new DataContext(string_to_connect).GetTable<Product>();
        }
        public IQueryable<Product> Products 
        {
            get { return pr_table; }
        }
    }
}

<%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<IEnumerable<WebApp.Models.Product>>" %>

<asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server">
	Products
</asp:Content>

<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">

    <% foreach (var product in Model){ %>
    
    <%=product.Name  %>
    <%=product.Description %>
    <%=product.Price.ToString("c") %>
    
    <%} %>

</asp:Content>

        public ViewResult List() 
        {
            return View((from a in i_pr_rep.Products where a.Name == "Kayak" select new Product { Name = a.Name, Description = a.Description, Category = a.Category, Price = a.Price }).ToList());
        }

      public ViewResult List() 
        {
            return View(i_pr_rep.Products.Where(a=>a.Name == "Kayak").ToList());
        }

return (from a in Category_table
                    where (a.ParentId == Id)
                    select a ).ToList();

        public IEnumerable<CategoryViewData> Get_category_list(int Id) 
        {
            return (from a in Category_table where (a.ParentId == Id) select new CategoryViewData{NameCategory = a.NameCategory, ParentId = a.ParentId});// Здесь перекидываем в DTO класс
        }

        public ActionResult List(int? Id)
        {
            int _id = Id ?? 0;
            Main_Linq_Aticles mla = new Main_Linq_Aticles();
            return View(mla.Get_category_list(_id));
            
        }

жаль, что вопросы привязки данных к View выходят за рамки тематики данного раздела...

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl" %>


<%{
    foreach (var item in ViewData["mostpopular"] as IEnumerable<ArticleTitle>)
    {%>
      <p>
<%=Html.RouteLink(
            item.Head,
            "Details",
            new
            {
              controller = "Article",
              action = "Details",
              id = item.ID
            })%>
      </p>
<% }
  }%>

public ActionResult List(int? Id)
        {
            int _id = Id ?? 0;
            Main_Linq_Aticles mla = new Main_Linq_Aticles();
            ViewData["category_list"] = mla.Get_category_list(_id);
            return View(ViewData);
            
        }

<%@ Page Title="" Language="C#" MasterPageFile="~/MasterPage.Master" Inherits="System.Web.Mvc.ViewPage<IEnumerable<Linq_Aticles.Models.CategoryViewData>>" %>

<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">

    

</asp:Content>

<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">

<% Html.RenderPartial("ViewUserControl1");  %>
</asp:Content>

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl" %>

<% foreach (var item in ViewData["category_list"] as IEnumerable<CategoryViewData> )
   { %>
   
   <%=item.NameCategory  %>
   <%=item.ParentId  %>
   
<% } %>

namespace Linq_Aticles.Models
{
    public class CategoryUnionViewData
    {
            public CategoryUnionViewData() { } // Конструктор
            public IEnumerable<CategoryViewData> cat_view_data { get; set; }
    }
}

   public ActionResult List(int? Id)
        {
            int _id = Id ?? 0;
            Main_Linq_Aticles mla = new Main_Linq_Aticles();
            CategoryUnionViewData ct = new CategoryUnionViewData();
            ct.cat_view_data = mla.Get_category_list(_id);
            return View(ct);
            
        }

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<IEnumerable<Linq_Aticles.Models.CategoryViewData>>" %>

<% foreach (var item in Model  )
   { %>
   
   <%=item.NameCategory  %>
   <%=item.ParentId  %>
   
<% } %>

%@ Page Title="" Language="C#" MasterPageFile="~/MasterPage.Master" Inherits="System.Web.Mvc.ViewPage<Linq_Aticles.Models.CategoryUnionViewData>" %>

<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">

    

</asp:Content>

<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">

<% Html.RenderPartial("ViewUserControl1",Model.cat_view_data);  %>
</asp:Content>

дык, здесь недалеко...