When you work on grouping data in Excel, the outline symbols will appear on the left indicating the groups of the data. It is helpful but if you want to get rid of it, please follow the steps below:
Step 1: Click the "File" Tab from the ribbon;
Step 2: Click "Options" from the left navigation menu;
Step 3: Click "Advanced" from the left navigation menu in the dialog box;
Step 4: Check "Show outline symbols if an outline is applied" under the section of "Display options for this worksheet";
Step 5: Click "OK" at the bottom to apply the changes.