I have a data, in which I have grouped some columns in excel file.
If I have to insert another set of data to excel file, EPp Plus code is recreating entire file and clearing existing grouped by columns.

I need to keep the existing grouped columns.

ExcelPackage.LicenseContext = LicenseContext.NonCommercial;
            using (var package = new ExcelPackage(new FileInfo(outputExcelPath)))
            {
                // Open or create the worksheet
                var sheet = package.Workbook.Worksheets["InvoiceDetails"];
                if (sheet == null)
                {
                    sheet = package.Workbook.Worksheets.Add("InvoiceDetails");
                    // Set up the header row for a new worksheet
                    SetupHeaderRow(sheet);
                }
           package.Save()
}