Can You Help Me In Sorting? How Can I Add Sorting?

<asp:GridView runat="server" CssClass="table table-striped table-bordered" AutoGenerateColumns="false"                                   
    Width="100%" ID="gvInvoices">
    <Columns>                                       
        <asp:BoundField DataField="branch_num" HtmlEncode="false" HeaderText="رقم المحطة<br/>Branch No" />                                       
        <asp:BoundField DataField="_date" HtmlEncode="false" HeaderText="التاريخ<br/>Date" />
        <asp:BoundField DataField="invoice_number" HtmlEncode="false" HeaderText="رقم الفاتورة<br/>Invoice No" />
        <asp:BoundField DataField="item" HtmlEncode="false" HeaderText="الصنف<br/>Gasoline Type" />
        <asp:BoundField DataField="machineID" HtmlEncode="false" HeaderText="رقم المكينة<br/>Machine ID" />
        <asp:BoundField DataField="payment_type" HtmlEncode="false" HeaderText="طريقة الدفع<br/>Payment Type" />
        <asp:BoundField DataField="price" HtmlEncode="false" HeaderText="السعر<br/>Price" />
        <asp:BoundField DataField="qty" HtmlEncode="false" HeaderText="الكمية<br/>Qty" />
        <asp:BoundField DataField="total" HtmlEncode="false" HeaderText="الإجمالي<br/>Total Amount" />
        <asp:BoundField DataField="userID" HtmlEncode="false" HeaderText="المستخدم<br/>User" />
        <asp:BoundField DataField="vat_amount" HtmlEncode="false" HeaderText="الضريبة<br/>VAT Amount" />
    </Columns>
    <PagerStyle HorizontalAlign="Center" CssClass="GridPager" />
    <HeaderStyle HorizontalAlign="Center" />                                  
</asp:GridView>

public class Root
{
  public string branch_num { get; set; }
  [JsonProperty("date")]
  public DateTime _date { get; set; }
  public string invoice_number { get; set; }
  public string item { get; set; }
  public string machineID { get; set; }
  public string payment_type { get; set; }
  public double price { get; set; }
  public double qty { get; set; }
  public double total { get; set; }
  public string userID { get; set; }
  public double vat_amount { get; set; }
}

private List<Root> GetDataFromJSON()
{
  ServicePointManager.Expect100Continue = true;
  ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;
  string json = (new WebClient()).DownloadString("https://fuel-station-d8853-default-rtdb.firebaseio.com/invoices-prod.json");
  JToken result = JsonConvert.DeserializeObject("[" + json + "]") as JToken;
  List<Root> roots = new List<Root>();
  foreach (var item in result)
  {
    JObject obj = JObject.Parse(item.ToString());
    foreach (var keypair in obj)
    {
      foreach (var keypair1 in JObject.Parse(keypair.Value.ToString()))
      {
        foreach (var item1 in JObject.Parse(keypair1.Value.ToString()))
        {
          roots.Add(JsonConvert.DeserializeObject<Root>(item1.Value.ToString()));
        }
      }
    }
  }
 
  return roots;
}

private void BindData()
{
    List<Root> roots = GetDataFromJSON();
 
    if (ddlBranchNumbers.SelectedIndex > 0)
    {
      roots = roots.Where(x => x.branch_num.EndsWith(ddlBranchNumbers.SelectedValue.Trim())).ToList();
    }
 
    if (ddlMachineNumbers.SelectedIndex > 0)
    {
      roots = roots.Where(x => x.machineID.EndsWith(ddlMachineNumbers.SelectedValue.Trim())).ToList();
    }
    gvInvoices.DataSource = roots;
    gvInvoices.DataBind();
    lblTotalRecords.Text = roots.Count.ToString();
  }
protected void Page_Load(object sender, EventArgs e)
{
    System.Web.UI.HtmlControls.HtmlGenericControl li = (System.Web.UI.HtmlControls.HtmlGenericControl)this.Page.Master.FindControl("Main_lnkmnu_Harqat_Fawatir");
    li.Attributes.Add("class", "menu single-menu active");
 
    if (!this.IsPostBack)
    {
      this.BindDropDownList();
      this.BindData();
    }
}