How to add expandable category menu to sidebar?

If you go to https://www.careermakersblog.com/wordpress , you’ll see a list of categories on the left hand side. I’m wanting to have an expandable menu so that I can have some categories remain ‘main’ categories, and others become ‘sub’ categories, that appear when the main category is moused over.

Does anyone know how to do this? And, if it’s not possible to find a plug-in for it that I can install myself, are there any really good wordpress tech people out there that I could pay to program it in for me?

Thanks in advance,

Sarah Woods