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:

• On the Chart Design tab, in the Data group, choose Select Data:
  
• Right-click on 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: