title: Can a child node be assigned back to its parent node in tree structure?
body: <p>As title, I'm currently trying to build a tree structure to take my topics/definitions and their related topics/definition into a tree for traversal and further analysis. The data look like this:</p>
  <pre><code>VR(root)
  |____electric vehicle
      |____electric car
          |____electric vehicle
          |____chain link
          |____marketing automation
      |____laser cutting
          |____performance marketing
          |____electric vehicle
          |____dental bonding
      |____performance marketing
          |____marketing automation
          |____call-tracking software
          |____PaaS
  </code></pre>
  <p>Problems are:</p>
  <p>(1)some topics are related back to other parent topics
  (2)some parents nodes share the same child nodes</p>
  <p>Is there any tree structure allows this, or is there any better way to map these data into any kind of graph that can be visualized?</p>