If you want something extremely bitter (and supposedly good against gastrointestinal diseases), you can boil some oak bark in water and drink it.

Oil from the Sassafras tree can taste amazing if you can chemistry.

Birch juice is also tasty.

I believe other trees do have sugary syrup. I saw a video of some guy collecting it in a plastic jug. I forget which kinda tree it was.

The rubber tree has entered the chat