title: Tree material angular 2 selected state
body: <p>I have a Angular 2 Material Tree when I click a node from the tree I need to have the selected state on that node to change the background color.
  I have no idea how I can do that. I didn't find nothing in documentation to help me. Here is the html code and a picture that how it should look the tree</p>
  
  <p><a href="https://i.stack.imgur.com/n04Or.png" rel="noreferrer"><img src="https://i.stack.imgur.com/n04Or.png" alt="That is how it should look the tree when clicking on a node"></a></p>
  
  <pre><code>       &lt;mat-tree [dataSource]="dataSource" [treeControl]="treeControl" #matTree [ngStyle]="{ 'color': red}"&gt;
          &lt;mat-tree-node *matTreeNodeDef="let node" matTreeNodeToggle matTreeNodePadding&gt;
            &lt;button mat-icon-button disabled&gt;&lt;/button&gt;
            {{node.filename}}
          &lt;/mat-tree-node&gt;
  
          &lt;mat-tree-node *matTreeNodeDef="let node;when: hasChild" matTreeNodePadding &gt;
            &lt;button mat-icon-button matTreeNodeToggle [attr.aria-label]="'toggle ' + node.filename" click="onClick()"&gt;
              &lt;mat-icon class="mat-icon-rtl-mirror"&gt;
                {{treeControl.isExpanded(node) ? 'expand_more' : 'chevron_right'}}
              &lt;/mat-icon&gt;
            &lt;/button&gt;
            {{node.filename}}
          &lt;/mat-tree-node&gt;
        &lt;/mat-tree&gt;
  </code></pre>