How to create an axis with subcategories
One of such tricks is showing an axis with subcategories:

To create an axis with subcategories, do one of the following:
- If you have a data with structured categories, just select them and create
the chart you like:
Excel automatically "understands" the structured data as axis data with subcategories:
- If you already have a chart, do the following:
For example:

1. Add the new category or subcategory to your data.
For this example:

2. Do one of the following:
- Under Chart Tools, on the Design tab, in the Data group, choose Select Data:
- Right-click in the chart area and choose Select Data... in the popup menu:
3. In the Select Data Source dialog box, under Horizontal (Category) Axis Labels, click the Edit button:

4. In the Axis Labels dialog box, choose cells with categories and subcategories for this axis and click OK several times:

Excel changes an axis:
