1. Select the data source and define the name

First, select the data area in the table, select the "Formula" tab in the toolbar above the table, and click the "Specify" button in the "Formula" tab to see the "Specify Name" dialog box. Check the check mark in front of "First Line". Just click "OK". As shown in Figure 1

      
Figure 1

2. Select the first row as the "Category" group

Next, select the first row of the data, select the "Name Manager" button in the "Formulas" tab, enter the name "Category", and then click "OK". Then select the first row as the "Category" group and you are done. As shown in Figure 2

      
Figure 2

3. Set up a first-level drop-down list

First select the range that needs to be filled with data, find the "Data" tab in the toolbar, click the "Validity" button to open the data validity dialog box, and select the "Settings" tab in the dialog box. Then select "Sequence" under "Allow", enter "=Category" in the box under Source, and finally click OK. The first level drop-down list is completed. As shown in Figure 3

      
Figure 3