code: def _populate_worksheet(self, workbook, worksheet):
          
          chart_num_format = workbook.add_format(
              {'num_format': self._chart_data.number_format}
          )
          for series in self._chart_data:
              series_num_format = (
                  workbook.add_format({'num_format': series.number_format})
              )
              offset = self.series_table_row_offset(series)
              # write X values
              worksheet.write_column(
                  offset+1, 0, series.x_values, chart_num_format
              )
              # write Y values
              worksheet.write(offset, 1, series.name)
              worksheet.write_column(
                  offset+1, 1, series.y_values, series_num_format
              )
              # write bubble sizes
              worksheet.write(offset, 2, 'Size')
              worksheet.write_column(
                  offset+1, 2, series.bubble_sizes, chart_num_format
              )
docs: Write chart data contents to *worksheet* in the bubble chart layout.
          Write the data for each series to a separate three-column table with
          X values in column A, Y values in column B, and bubble sizes in
          column C. Place the series label in the first (heading) cell of the
          values column.