title: Animated TreeView and nested Accordions
body: <p>I want to achive a Navigation for my application that looks like a TreeView but is animated like a TitledPane. That is, a Transition when expanding/collapsing an item for its content.</p>
  
  <p>What I did so far is to nest multiple Accordions like this:</p>
  
  <pre><code>- TopAccordion
  ---- TitledPane
  ------- Accordion
  ----------TitledPane
  ----------TitledPane
  ----------TitledPane
  ---- TitledPane
  ------- Accordion
  ----------TitledPane
  ----------TitledPane
  ----------TitledPane
  </code></pre>
  
  <p>etc. Unfortunately, this results in same ugly transitions (notice the large gap when opening a nested TitledPane):</p>
  
  <p><img src="https://i.stack.imgur.com/tUKjL.png" alt="enter image description here"></p>
  
  <p>Is there a way to animate TreeViews and how? I couldn't find a way to do it by looking at the TreeCell/TreeItem API.</p>
  
  <p>Regards,
  Sebastian</p>