Workaround:
private void radButton1_Click(object sender, EventArgs e)
{
    var allNodes = radTreeView1.TreeViewElement.GetNodes().ToList();

    int row = 0;
  
    Workbook workbook = new Workbook();
    Worksheet newWorksheet = workbook.Worksheets.Add();

    foreach (var item in allNodes)
    {

        CellSelection cell = newWorksheet.Cells[row, item.Level];
        cell.SetValue(item.Text);

        cell = newWorksheet.Cells[row++, 2];
        cell.SetValue(item.Checked);

    }

    var formatProvider = new XlsxFormatProvider();


    var bytes = formatProvider.Export(workbook);
    File.WriteAllBytes(@"D:\Test.xlsx", bytes);


}