To change the direction of the group/outline function in Excel, you can follow these steps:

1. Select the columns that you want to group together. In your case, select columns 5-8, 9-12, 13-16, and 17-20.
2. Click on the "Data" tab in the ribbon at the top of the Excel window.
3. Click on the "Group" button in the "Outline" section of the ribbon.
4. In the "Group" dialog box that appears, select the "Rows" option instead of the default "Columns" option.
5. Click on the "OK" button to group the selected columns as rows.
6. Now, you should see the outline symbols appear on the left side of the worksheet, indicating the grouped rows.
7. To collapse or expand the grouped rows, click on the small plus or minus symbols in the outline symbols.

By grouping the columns as rows, you can achieve the desired cascade effect from left to right. As you add more columns to the right side of the worksheet, you can continue to group them as rows to maintain the same outline direction.