title: Explain why insertion (and the different cases) don't change black height of red black trees
body: <p><a href="https://i.stack.imgur.com/aEgGJ.png" rel="nofollow noreferrer">red black tree - insertion - z's uncle is red</a></p>
  
  <p>Why is black height of node γ(gamma, the top most node) is unchanged after the operation?</p>
  
  <p>I know how to explain why black height of T1 - T4 is the same after operation. But for gamma, I have absolutely no clue.</p>
  
  <p>Anyone has ideas?</p>