title: Material-UI TreeView TreeItems background
body: <p>I don't know if it's bug or feature, when I used these dependacies:</p>
  <pre><code>&quot;@material-ui/core&quot;: &quot;4.8.3&quot;,
  &quot;@material-ui/lab&quot;: &quot;4.0.0-alpha.37&quot;
  </code></pre>
  <p>After losing focus from some TreeItem and selecting another TreeItem, I didnt see any TreeItem backgroud on TreeItems selected previously.</p>
  <p><a href="https://i.stack.imgur.com/ayyJJ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ayyJJ.png" alt="before" /></a></p>
  <p>Now, after updating to:</p>
  <pre><code>&quot;@material-ui/core&quot;: &quot;^4.11.3&quot;
  &quot;@material-ui/lab&quot;: &quot;^4.0.0-alpha.57&quot;
  </code></pre>
  <p>I can see some light blue background on TreeItems, that were selected to node expending.
  <a href="https://i.stack.imgur.com/Baz5s.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Baz5s.png" alt="enter image description here" /></a>
  So maybe it's some new feature, and someone know how to disable it?</p>