title: Print tree with indentations
body: <p>I want to print out a simple tree that describes a band. I start by creating a node called "Band" and then I make the child "Wind instruments" which in turns have the children "Saxophone" and "Trumpet". Then I make a sibling to "Wind instruments" called "Song" and so on. The code is pretty straightforward: </p>
  
  <pre><code>class Node:                                     
      value = ""
      down = None
      right = None
  def write(p):
      if p==None:
          return
      print(p.value)
      if p.down!=None:        #My idea is that if we go down the tree, we indent first
          print("    ",end="")     
          write(p.down)
      write(p.right)      #If we don't go down, we simply write out the siblings
  a=Node()
  a.value="Band"
  a.down=Node()
  a.down.value="Wind instruments"
  a.down.down=Node()
  a.down.down.value="Saxophone"
  a.down.down.right=Node()
  a.down.down.right.value="Trumpet"
  a.down.right=Node()
  a.down.right.value="Song"
  a.down.right.right=Node()
  a.down.right.right.value="String instruments"
  a.down.right.right.down=Node()
  a.down.right.right.down.value="Guitar"
  a.down.right.right.down.right=Node()
  a.down.right.right.down.right.value="Bass"
  write(a)
  </code></pre>
  
  <p>The output is:</p>
  
  <pre><code>Band
      Wind instruments
      Saxophone
  Trumpet
  Song
  String instruments
      Guitar
  Bass
  </code></pre>
  
  <p>But I want the output to be:</p>
  
  <pre><code>Band
      Wind instruments
          Saxophone
          Trumpet
      Song
      String instruments
          Guitar
          Bass
  </code></pre>
  
  <p>Anyone have an idea how to achieve this? </p>