cannot push data to array

I have to enter the URL twice to see the data. What happened?

1.array keep data form fucntion createTree() for t.addNode(), output t.getNode() to display

var Tree = function() {
    this.node = [];
}
Tree.prototype.addNode = function(value) {
    this.node.push(value);
}
Tree.prototype.getNode = function() {
    return this.node;
}
Tree.prototype.reset = function() {
    this.node = [];
}

calling array var t = new Tree();

2.craete tree

function createTree(root, level = 0) {
    if (level < 6) {
        async.waterfall([
            function(cb) {
                Member.find({ sponsor: root }, function(err, member) {
                    return cb(null, member);
                });
            },
            function(member, cb) {
                if (member.length < 1) ? return 0 : return cb(null, member);
            }
        ], function(err, data) {
            if (!err) {
                level += 1;
                data.map(function(item) {
                    t.addNode(item);
                    createTree(item._id, level);
                });
            }
        });
    }
}

3.url params in express

exports.getReferralTable = function(req, res) {
    async.waterfall([
        function(cb) {
            t.reset();
            createTree(req.params._id);
            return cb(null);
        },
        function(cb) {
            return cb(null, t.getNode());
        },
    ], function(err, data) {
        if (err) {
            res.json(err);
        } else {
            res.json(data);
        }
    });
}

how fix this problem

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