Hidden Drop down in Form

I’m trying to incorporate a drop down function in a form. It should correspond to the following framework first drop down function selection one of 10 services → when this is selected → a hidden dropdown should appear with the selection of more information and book a call → when selecting more information a button should appear that goes to the landing page from the service → if you select book a call, a lead generation form should open. Does anyone know how to implement this?