title: AG-Grid sorting is not working with TreeData
body: <p>I have an ag-grid with <strong>Tree Data</strong>. (<a href="https://www.ag-grid.com/javascript-grid-tree/" rel="nofollow noreferrer">https://www.ag-grid.com/javascript-grid-tree/</a>). </p>
  
  <p>I am facing an issue that column is being sorted in lexicographical order instead of Asc/Desc. For number columns, it should be sorted by max/min value. Here is the JsFiddle link: <a href="https://jsfiddle.net/pbjqdw6w" rel="nofollow noreferrer">https://jsfiddle.net/pbjqdw6w</a> and see the behavior of <strong>Currency</strong> column.</p>
  
  <p><code>enableSorting: true</code></p>