Insert multiple records in one transaction

protected void btnSubmit_click(object sender, EventArgs e)
    {
        try
        {
            using ( dbmodel dbContext = new dbmodel())
            {
                GoodsInDetails gdin = new GoodsInDetails();
                gdin.GoodsInID = int.Parse(txtorderID.Text);
                gdin.ProductID = int.Parse(txtbox1.Text);
                //**Add ProductID x amount of times dependednt on value in
                //txtQuanitity.text;***

                dbContext.Add(gdin);
                dbContext.SaveChanges();
                lblMessage.Text = "Succesfully added!";
            }
        }
        catch (Exception ex)
        {
            lblMessage.Text = ex.Message;
        }
    }
}