title: Angular Material 6.0.1 Tree default opened and expand/collapse all
body: <p>I'm using the Angular Material Tree in my project.
  Is it possible to have the tree opened by default.</p>
  
  <p>And could there be a way to expand/collapse all the nodes at once (eg. with a button)</p>
  
  <p><a href="https://material.angular.io/components/tree/overview" rel="noreferrer">https://material.angular.io/components/tree/overview</a></p>