将php数组转换为json树视图

我有一个json，如下所示：（这是用于通过ajax加载树视图的treeview jquery插件）

[
{
    "text": "1. Pre Lunch (120 min)",
    "expanded": true,
    "classes": "important",
    "children":
    [
        {
            "text": "1.1 The State of the Powerdome (30 min)"
        },
         {
            "text": "1.2 The Future of jQuery (30 min)"
        },
         {
            "text": "1.2 jQuery UI - A step to richnessy (60 min)"
        }
    ]
},
{
    "text": "2. Lunch  (60 min)"
},
{
    "text": "3. After Lunch  (120+ min)",
    "children":
    [
        {
            "text": "3.1 jQuery Calendar Success Story (20 min)"
        },
         {
            "text": "3.2 jQuery and Ruby Web Frameworks (20 min)"
        },
         {
            "text": "3.3 Hey, I Can Do That! (20 min)"
        },
         {
            "text": "3.4 Taconite and Form (20 min)"
        },
         {
            "text": "3.5 Server-side JavaScript with jQuery and AOLserver (20 min)"
        },
         {
            "text": "3.6 The Onion: How to add features without adding features (20 min)",
            "id": "36",
            "hasChildren": true
        },
         {
            "text": "3.7 Visualizations with JavaScript and Canvas (20 min)"
        },
         {
            "text": "3.8 ActiveDOM (20 min)"
        },
         {
            "text": "3.8 Growing jQuery (20 min)"
        }
    ]
}
]

我想写一个php数组，它返回这样的json。请帮帮我。

我尝试了几种方法，但都做不到。