Wow thanks so much for taking the time to make this guide.
I ran into trouble with the GUI at the very end (the enum Tree objects were giving me trouble back in my main class).
But here's how I fixed it in case anyone runs into the same issue:
I deleted the enum and changed the Tree objects into Strings. Then just add the Strings individually into the JComboBox.
GUI Class:
Main Class:
(i know this may be less efficient/elegeant/conventional... but it seemed much more beginner-friendly to me)