  One of the fundamental properties of the Mandelbrot set is that the set of
postcritically finite parameters is structured like a tree. We extend this
result to the set of quadratic kneading sequences and show that this space
contains no irrational decorations.
  Along the way, we prove a combinatorial analogue to the correspondence
principle of dynamic and parameter rays. Our key tool is to work simultaneously
with the two equivalent combinatorial concepts of Hubbard trees and kneading
sequences.
