How to add a custom button in echart toolbox such that clicking on it should add a new series in linechart?

Question

I want a drop down in the echart toolbox such that I can select series to be shown. In the example, the drop-down should contain [Email, Union Ads, Video Ads, Direct, Search Engine] and the user should be able to select one or more. How can I achieve this?

Echart example

Note: My usecase is to show the dropdown with the list and on selection it will get the data from DB via sql.