title: List directory tree structure in python?
body: <p>I know that we can use <code>os.walk()</code> to list all sub-directories or all files in a directory. However, I would like to list the full directory tree content:</p>
  
  <pre><code>- Subdirectory 1:
     - file11
     - file12
     - Sub-sub-directory 11:
           - file111
           - file112
  - Subdirectory 2:
      - file21
      - sub-sub-directory 21
      - sub-sub-directory 22    
          - sub-sub-sub-directory 221
              - file 2211
  </code></pre>
  
  <p>How to best achieve this in Python?</p>