Comment by quantadev
The original "Block Editor" (that Jupyter modeled itself after) is the one that's now called "Quanta", and has been around for decades in various forms and incantations:
https://github.com/Clay-Ferguson/quantizr
I'm thinking that Jupyter might still not be "Tree Based" but that would be a heck of a leap in capability if they "fix" that.
I always thought Jupyter was based on other notebook-style interfaces like Mathematica or Maple.