树商店没有加载

Question

我是sencha Extjs的新手，尝试动态加载树数据，但我的树没有加载

我的商店如下：

root:{
    //field:'Total',
    expanded: true,
    trade:'Total',
    text:'Total',
    children:['childs']
},
proxy:{
    type:'direct',
    directFn:type.getTreeData,
    root:'trade'
}

和我的json回复如下：

[{"trade":"Market","childs":[
    {"childTrade":"bc","value":125.23},
    {"childTrade":"AndhraBank","value":14.25},
    {"childTrade":"ABC","value":78.36}]
},{"trade":"Electronincs","childs":[
    {"childTrade":"klo","value":125.23},
    {"childTrade":"bank","value":14.25},
    {"childTrade":"KBC","value":78.36}]
}]