public ActionResult Add(string serial, string correlative, string customer, string NIT, string date, string purchaseDescription, string total)
        {
            BinaryTree <Invoice> InvoiceTree;

            if (Session["InvoiceTree"] != null)
            {
                InvoiceTree = (BinaryTree <Invoice>)Session["InvoiceTree"];
            }
            else
            {
                InvoiceTree = new BinaryTree <Invoice>();
            }

            Invoice InvoiceObj = null;

            if (serial != null)
            {
                InvoiceObj = new Invoice(serial, correlative, customer, NIT, date, purchaseDescription, total);
            }
            else
            {
                InvoiceObj = new Invoice(correlative, customer, NIT, date, purchaseDescription, total);
            }

            InvoiceTree.Insert(InvoiceObj, Invoice.compareInvoices);

            Session["InvoiceTree"] = InvoiceTree;
            return(View("Index", Session["InvoiceTree"]));
        }
        [HttpPost] //Since user is retrieving data
        public ActionResult ReadInvoice(HttpPostedFileBase uploadedFile)
        {
            BinaryTree <Invoice> InvoiceTree;

            // If there's already a tree, we work on it. Otherwise, we create a new one.
            if (Session["InvoiceTree"] != null)
            {
                InvoiceTree = (BinaryTree <Invoice>)Session["InvoiceTree"];
            }
            else
            {
                InvoiceTree = new BinaryTree <Invoice>();
            }


            if (uploadedFile == null)
            {
                return(View("Index"));
            }

            StreamReader reader = new StreamReader(uploadedFile.InputStream);
            string       line   = "";

            if (uploadedFile != null && uploadedFile.ContentLength > 0)
            {
                while ((line = reader.ReadLine()) != null)
                {
                    var information = line.Split(',');

                    Invoice InvoiceObj = null;
                    if (information.Length == 7) //means there's specific serial in the parameters
                    {
                        int total = -1;
                        //Data validation
                        try
                        {
                            total = int.Parse(information[6]);
                        }
                        catch (Exception)
                        {
                        }
                        InvoiceObj = new Invoice(information[0], information[1], information[2], information[3], information[4], information[5], information[6]);
                    }
                    else if (information.Length == 6) // means no serial in the parameteres, there will be a random one.
                    {
                        int total = -1;
                        //Data validation
                        try
                        {
                            total = int.Parse(information[7]);
                        }
                        catch (Exception)
                        {
                        }
                        InvoiceObj = new Invoice(information[0], information[1], information[2], information[3], information[4], information[5]);
                    }

                    InvoiceTree.Insert(InvoiceObj, (Invoice x, Invoice y) => (x.serial + x.correlative).CompareTo(y.serial + y.correlative));
                }
            }

            Session["InvoiceTree"] = InvoiceTree;
            return(View("Index", Session["InvoiceTree"]));
        }