如何在ui-tree angular js中的顶部添加新节点

<div ui-tree>
  <ol ui-tree-nodes ng-model="treeData">
    <!-- 树节点的循环 -->
    <li ng-repeat="node in treeData" ui-tree-node>
      <!-- 节点内容 -->
      <div ui-tree-handle>
        {{node.name}}
      </div>
      <!-- 子节点 -->
      <ol ui-tree-nodes ng-model="node.children" ng-class="{hidden: collapsed}">
        <li ng-repeat="childNode in node.children" ui-tree-node>
          <div ui-tree-handle>
            {{childNode.name}}
          </div>
          <ol ui-tree-nodes ng-model="childNode.children" ng-class="{hidden: collapsed}">
            <!-- 可以继续嵌套子节点 -->
          </ol>
        </li>
      </ol>
    </li>
  </ol>
</div>

$scope.treeData = [];

$scope.addTopNode = function() {
  var newNode = {
    name: "New Node",
    children: []
  };
  $scope.treeData.unshift(newNode);
};

<button ng-click="addTopNode()">添加顶部节点</button>