What does every root is at the same level mean My textbook says a "complete binary tree" is a "full binary tree" where every root is at the same level. 

My conceptual understanding:

All this time, I was led by my textbook to believe a root is the "top-most vertex" in which all the other vertex are led away from it. So basically I am led to believe there can be only one root in a tree. 

Questions:

What does "where every root is at the same level" even mean? 

Isn't a root suppose to be at level 0 all the time?
It basically is a typo, every leaf at same level may be the correct words