read excel files with officeopenxml in csharp

main.cs
using DocumentFormat.OpenXml.Packaging;
using DocumentFormat.OpenXml.Spreadsheet;

public static List<List<string>> ReadExcelFile(string filePath)
{
    List<List<string>> rows = new List<List<string>>();

    using (SpreadsheetDocument spreadsheetDocument = SpreadsheetDocument.Open(filePath, false))
    {
        WorkbookPart workbookPart = spreadsheetDocument.WorkbookPart;
        WorksheetPart worksheetPart = workbookPart.WorksheetParts.First();
        SheetData sheetData = worksheetPart.Worksheet.Elements<SheetData>().First();

        foreach (Row row in sheetData.Elements<Row>())
        {
            List<string> cells = new List<string>();

            foreach (Cell cell in row.Elements<Cell>())
            {
                cells.Add(GetCellValue(workbookPart, cell));
            }

            rows.Add(cells);
        }
    }

    return rows;
}

private static string GetCellValue(WorkbookPart workbookPart, Cell cell)
{
    SharedStringTablePart sharedStringPart = workbookPart.SharedStringTablePart;

    if (cell.DataType != null && cell.DataType.Value == CellValues.SharedString)
    {
        return sharedStringPart.SharedStringTable.ChildElements[Int32.Parse(cell.InnerText)].InnerText;
    }
    else
    {
        return cell.InnerText;
    }
}
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