private void AddColumns(SpreadsheetDocument doc, string sheetName)
{
var sheetData = doc.GetSheetDataByName(sheetName);
var headerRow = sheetData.Descendants<Row>().FirstOrDefault();
if (headerRow == null) return;
var colCount = headerRow.Descendants<Cell>().Count();
var columnRange = Enumerable.Range(0, colCount).Select(i => CreateColumn(doc, sheetData, i));
var columns = new Columns(columnRange);
var sheet = doc.GetWorksheetByName(sheetName);
sheet.InsertAt(columns, 0);
}