private static void WriteExcelFile(DataTable dt, SpreadsheetDocument spreadsheet)
        {
            //  Create the Excel file contents.  This function is used when creating an Excel file either writing 
            //  to a file, or writing to a MemoryStream.
            spreadsheet.AddWorkbookPart();
            if (spreadsheet.WorkbookPart == null) return;
            spreadsheet.WorkbookPart.Workbook = new Workbook();

            var definedNamesCol = new DefinedNames();

            // The following line of code (which prevents crashes in Excel 2010)
            spreadsheet.WorkbookPart.Workbook.Append(new BookViews(new WorkbookView()));

            //  If we don't add a "WorkbookStylesPart", OLEDB will refuse to connect to this .xlsx file !
            var workbookStylesPart = spreadsheet.WorkbookPart.AddNewPart<WorkbookStylesPart>("rIdStyles");
            workbookStylesPart.Stylesheet = GenerateStyleSheet();
            workbookStylesPart.Stylesheet.Save();



            var sheets = spreadsheet.WorkbookPart.Workbook.AppendChild(new Sheets());
            //  For each worksheet you want to create
            var worksheetName = dt.TableName;

            //  Create worksheet part, and add it to the sheets collection in workbook
            var worksheetPart = spreadsheet.WorkbookPart.AddNewPart<WorksheetPart>();


            SheetData sheetData = new SheetData();

            //add the first row
            Row firstRow = new Row();
            firstRow.RowIndex = (UInt32)1;

            //create a cell in A1 (the upper left most cell of the merged cells)
            Cell dataCell = new Cell();
            dataCell.CellReference = "A1";
            CellValue cellValue = new CellValue();
            cellValue.Text = "Raw Matrials and Price List";
            dataCell.Append(cellValue);
            firstRow.AppendChild(dataCell);
            sheetData.AppendChild(firstRow);

            //add the second row
            Row secondrow = new Row();
            secondrow.RowIndex = (UInt32)2;
            //create a cell in A2 (the upper left most cell of the merged cells)
            Cell secdataCell = new Cell();
            secdataCell.CellReference = "A2";
            CellValue seccellValue = new CellValue();
            seccellValue.Text = "From: 121";

            Cell secdataCell2 = new Cell();
            secdataCell2.CellReference = "C2";
            CellValue seccellValue2 = new CellValue();
            seccellValue2.Text = "To: 250";

            secdataCell.Append(seccellValue);
            secdataCell2.Append(seccellValue2);
            secondrow.AppendChild(secdataCell);
            secondrow.AppendChild(secdataCell2);
            sheetData.AppendChild(secondrow);

            //based on the table data to add row and cell. 
            DocumentFormat.OpenXml.Spreadsheet.Row headerRow = new DocumentFormat.OpenXml.Spreadsheet.Row();
            List<String> columns = new List<string>();
            foreach (System.Data.DataColumn column in dt.Columns)
            {
                columns.Add(column.ColumnName);

                DocumentFormat.OpenXml.Spreadsheet.Cell cell = new DocumentFormat.OpenXml.Spreadsheet.Cell();
                cell.DataType = DocumentFormat.OpenXml.Spreadsheet.CellValues.String;
                cell.CellValue = new DocumentFormat.OpenXml.Spreadsheet.CellValue(column.ColumnName);
                headerRow.AppendChild(cell);
            }
            sheetData.AppendChild(headerRow);
            foreach (System.Data.DataRow dsrow in dt.Rows)
            {
                DocumentFormat.OpenXml.Spreadsheet.Row newRow = new DocumentFormat.OpenXml.Spreadsheet.Row();
                foreach (String col in columns)
                {
                    DocumentFormat.OpenXml.Spreadsheet.Cell cell = new DocumentFormat.OpenXml.Spreadsheet.Cell();
                    cell.DataType = DocumentFormat.OpenXml.Spreadsheet.CellValues.String;
                    cell.CellValue = new DocumentFormat.OpenXml.Spreadsheet.CellValue(dsrow[col].ToString()); //
                    newRow.AppendChild(cell);
                }
                sheetData.AppendChild(newRow);
            }

            // Add a WorkbookPart to the document.
            worksheetPart.Worksheet = new Worksheet(sheetData);

            //set the columns width
            Columns exccolumns = new Columns();

            exccolumns.Append(new Column() { Min = 1, Max = 2, Width = 20, CustomWidth = true });
            exccolumns.Append(new Column() { Min = 3, Max = 4, Width = 50, CustomWidth = true });

            worksheetPart.Worksheet.Append(exccolumns);

            //create a MergeCells class to hold each MergeCell
            MergeCells mergeCells = new MergeCells();

            //append a MergeCell to the mergeCells for each set of merged cells
            mergeCells.Append(new MergeCell() { Reference = new StringValue("A1:d1") });
            mergeCells.Append(new MergeCell() { Reference = new StringValue("A2:b2") });
            mergeCells.Append(new MergeCell() { Reference = new StringValue("c2:d2") });

            worksheetPart.Worksheet.InsertAfter(mergeCells, worksheetPart.Worksheet.Elements<SheetData>().First());

            var sheet = new Sheet
            {
                Id = spreadsheet.WorkbookPart.GetIdOfPart(spreadsheet.WorkbookPart.WorksheetParts.First()),
                SheetId = 1,
                Name = worksheetName
            };

            // If you want to define the Column Widths for a Worksheet, you need to do this *before* appending the SheetData
            // http://social.msdn.microsoft.com/Forums/en-US/oxmlsdk/thread/1d93eca8-2949-4d12-8dd9-15cc24128b10/

            sheets.Append(sheet);


            //  Append this worksheet's data to our Workbook, using OpenXmlWriter, to prevent memory problems
            //WriteDataTableToExcelWorksheet(dt, worksheetPart, definedNamesCol);
            spreadsheet.WorkbookPart.Workbook.Append(definedNamesCol);
            spreadsheet.WorkbookPart.Workbook.Save();
        }