Razor code

    var productForm = new FormModel(DataSourceType.SQLite, "northwind", "Products") { LayoutColumns = 3 };
    productForm.Columns = new List() 
    {
        new FormColumn("ProductID","ID") { DataOnly = true},
        new FormColumn("ProductName", "Name") {Required = true, MinLength = 3, MaxLength = 20 },
        new FormColumn("SupplierID","Supplier") { Lookup = new Lookup("Suppliers", "SupplierId", "CompanyName"),Required = true },
        new FormColumn("CategoryID","Category") { Lookup = new Lookup("Categories", "CategoryID", "CategoryName"),Required = true, HelpText = "Select a category for the product" },
        new FormColumn("QuantityPerUnit", "Qty"){ InitialValue = 0},
        new FormColumn("UnitPrice", "Price") {Required = true,InitialValue = 0, MinValue = 0.00, MaxValue = 100.00, Format = "c" },
        new FormColumn("UnitsInStock", "Stock") {Required = true,InitialValue = 0, MinValue = 0, MaxValue = 1000 },
        new FormColumn("UnitsOnOrder", "On Order") {Required = true,InitialValue = 0, MinValue = 0, MaxValue = 1000 },
        new FormColumn("ReorderLevel", "Re-order Level") {Required = true,InitialValue = 0, MaxValue = 50, LookupRange = Enumerable.Range(0,50) },
        new FormColumn("Discontinued") {DataType = typeof(bool), InitialValue = true, HelpText = "Discontinued products must have a re-order level of 0"}
    };

    productForm.FixedFilter = "ProductID = @ProductID";
    productForm.FixedFilterParameters.Add(new DbParameter("ProductID", -1));
    productForm.Bind(FormClientEvent.Initialised, "saveFormReference");

    var productsLevel = new TreeModel("Products");
    productsLevel.Columns = new List() 
    {
        new TreeColumn("ProductID") { PrimaryKey = true },
        new TreeColumn("ProductName"),
        new TreeColumn("CategoryID") { ForeignKey = true }
    };

    productsLevel.FixedFilter = "discontinued = @discontinued";
    productsLevel.FixedFilterParameters.Add(new DbParameter("discontinued", 0));
    var categoryProductTree = new TreeModel(DataSourceType.SQLite, "northwind", "Categories");
    categoryProductTree.Columns = new List()
    {
        new TreeColumn("CategoryID") { PrimaryKey = true },
        new TreeColumn("CategoryName")
    };

    categoryProductTree.NestedLevel = productsLevel;
    categoryProductTree.SelectionTitle = "Selected Product";
    categoryProductTree.ClientEvents[TreeClientEvent.Initialised] = "saveTreeReference";
    categoryProductTree.ClientEvents[TreeClientEvent.ItemSelected] = "productSelected";
    categoryProductTree.Expand = true;

    <div style="display:flex;flex-direction:column;gap: 4px;">
        <div style="display:flex;flex-direction:row;gap: 4px;">
            <div>
                <label style="margin-left:5px">Discontinued</label>
            </div>
            <div>
                <label><input type="checkbox" id="discontinued" /></label>
            </div>
        </div>
        <div>
            @(await DbNetSuiteCore.Control.Create(HttpContext).Render(categoryProductTree))
        </div>
        <div>
            @(await DbNetSuiteCore.Control.Create(HttpContext).Render(productForm))
        </div>
    </div>