You open a Graphical User interface browser, such as standard Google Chrome or Firefox, on the same machine as you are running the notebook server and put that URL in your browser address bar.
In your example, it is:
http://localhost:8000/treee?token=<THE_LONG_TOKEN_NUMBER>
The issue is you seem to be triggering a text based browser that doesn’t work with Jupyter.
Someone else posted a very similar screenshot here. In that case they didn’t actually share early on that they are using a remote server machine to run the notebook and that the wanted to access it with their local computer. And so if you aren’t doing that,the solutions they needed WILL NOT apply. (What I posted above will apply if you are trying to run the notebook and the browser on the exact same machine. In other words ALL LOCAL, same physical machine.) If using a remote machine is your situation, you’ll want to pay attention to that linked thread with the similar screenshot.