Every time you hit regenerate or edited a prompt in ChatGPT, you made a side conversation. ChatGPT kept only the last one on screen. Your export still has all of them, and GPTree now turns each one into a branch.
The conversation opens on the path you last used in ChatGPT, with the other paths beside it, ready to compare. Very heavily regenerated threads are capped, so a message regenerated fifty times will not produce fifty branches.