[DefaultValue(-1)]
[Parameter]
public int Level { get; set; }

<DxTreeView Data="@Data">
    <DataMappings>
        <DxTreeViewDataMapping Text="CategoryName" Children="Products"/>
        <DxTreeViewDataMapping Level="1" Text="ProductName"/>
    </DataMappings>
</DxTreeView>

@code {
    public IEnumerable<ProductCategory> Data => new List<ProductCategory>() {
        new ProductCategory() { CategoryName = "Bikes", Products = {
                new Product { ProductName = "Mountain Bikes" },
                new Product { ProductName = "Road Bikes" },
                new Product { ProductName = "Touring" }
            }
        },
        new ProductCategory() { CategoryName = "Components", Products = {
                new Product { ProductName = "Handlebars" },
                new Product { ProductName = "Bottom Brackets" },
                new Product { ProductName = "Brakes" },
                new Product { ProductName = "Chains" }
            }
        },
        new ProductCategory() { CategoryName = "Clothing", Products = {
                new Product { ProductName = "Bib-Shorts" },
                new Product { ProductName = "Caps" },
                new Product { ProductName = "Gloves" }
            }
        }
    };

    public class ProductCategory {
        public string CategoryName { get; set; }
        public List<Product> Products { get; } = new List<Product>();
    }

    public class Product {
        public string ProductName { get; set; }
    }
}