filterable.extra Boolean (default: true)

If set to true, the filter menu will allow the user to input a second criteria.

Example - disabling the extra filtering criteria

<div id="treelist"></div>
<script>
  $("#treelist").kendoTreeList({
    columns: [
      { field: "lastName" },
      { field: "position" },
      { field: "extension" }
    ],
    dataSource: [
      { id: 1, parentId: null, lastName: "Jackson", position: "CEO", extension: 8241 },
      { id: 2, parentId: 1, lastName: "Weber", position: "  VP, Engineering", extension: 8342 }
    ],
    filterable: {
      extra: false
    }
  });
</script>