zTree異步加載自動展開

最近在處理一個樹形菜單，要作到異步加載、自動展開。可怎麼搞都不行，要點擊一下才能展開全部。

使用的zTree版本是v3.5.18。其實仍是蠻簡單的。話很少說，代碼以下：

/**
 * 初始化菜單
 */
var initTree = function(treeId) {
    var settings = {
            treeId: treeId,
            async: {
                enable: true,
                type: 'post',
                dataType: 'json',
                url: 'menu/getMenusByParentId',
                // 查詢子菜單參數，傳父節點id、以及父節點是否爲葉子。葉子節點將再也不查詢，提升性能
                autoParam: ["id=parent_id", "is_leaf"], 
                dataFilter: function(treeId, parentNode, responseData) {
                    if(responseData) {
                        for(var i = 0, length = responseData.length; i < length; i++) {
                            var node = responseData[i];
                            if(node.is_leaf == 0) {//節點的isParent=true，纔會異步加載子節點
                                node.isParent = true;
                            }
                        }
                    }
                    
                    return responseData;
                }
            },
            callback: {                    
                onAsyncSuccess: function(event, treeId, treeNode, msg){
                // 此回調函數可逐級異步展開子節點
                    if(treeNode.isParent == true && treeNode.children 
                        && treeNode.children.length > 0) {
                        var children = treeNode.children;                        
                        for(var i = 0, length = children.length; i < length; i++) {
                            zTreeObj.reAsyncChildNodes(children[i], "refresh", false); 
                        }
                        zTreeObj.expandNode(treeNode, true);
                    }
                }
            }
    };
    
    var rootNode = {name:"菜單", murl:'', isParent: true, open:false, id: 0, is_leaf: 0};
    var zTreeObj = $.fn.zTree.init($("#"+treeId), settings, rootNode);
    // 異步加載樹.這裏要注意：直接傳rootNode異步刷新樹，將沒法展開rootNode。
    // 要經過以下方式獲取根節點。false參數展開本節點
    zTreeObj.reAsyncChildNodes(zTreeObj.getNodes()[0], "refresh", false);        
};