Refresh ASP.Net GridView data after insert using C#

I have a GridView and a submit button on the same page. Please each time i submit data to the database it does not reflect on the grid view immediately.

I have to refresh the page manage manually first.

Please help

What i have tried

public partial class Setting : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            BindUserDetails();
        }

        MainView.ActiveViewIndex = 0;
    }

    protected void BindUserDetails()
    {
        string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
        using (SqlConnection con = new SqlConnection(constr))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter("Select id, category FROM AssetsCategory ORDER BY id ASC", con))
            {
                using (DataTable dt = new DataTable())
                {
                    sda.Fill(dt);
                    gvDetails.DataSource = dt;
                    gvDetails.DataSource = dt;
                    gvDetails.DataBind();
                }
            }
        }
    }
    protected void Button4_Click(object sender, EventArgs e)
    {
        string insertSQL;
        insertSQL = "INSERT INTO AssetsCategory (";
        insertSQL += "Category)";
        insertSQL += "VALUES('";
        insertSQL += TextBox4.Text + "')";
        String connectionString = "Data Source=NER\SQLEXPRESS01; Initial Catalog= kaging;Integrated Security=True";
        SqlConnection con = new SqlConnection(connectionString);
        SqlCommand cmd = new SqlCommand(insertSQL, con);
        int added = 0;

        try
        {
            con.Open();
            added = cmd.ExecuteNonQuery();
            if (added == 1)
            {
                MainView.ActiveViewIndex = 1;
            }
            else
            {
                Label5.Text = "Error @ unit 7";
            }
        }
        catch (Exception err)
        {
            Response.Write(err.ToString());
        }
        finally
        {
            con.Close();
        }
    }
}