I tend to work this way with a tool called Markmap (https://markmap.js.org/repl). I start with one heading and a list then begin moving items and adding new headings/subheadings as the relationships form. For example:

 // Start with: # Ideas - Item 1 - Item 2 - Item 3 - Item 4 - Item 5 - Item 6 // Move to: # Ideas ## Group 1 - Item 1 - Item 2 - Item 3 ## Group 2 - Item 4 - Item 5 - Item 6