treepanel 传参数 高手 指教 ？？？？？？

var tree = new Tree.TreePanel({ 
        el:'tree',
//          region:'center',        
        useArrows:true,    
        autoScroll:true, 
        rootVisible:true,//是否显示根节点
        animate:true,    
        enableDD:true,    
        containerScroll: true,     
        loader: new Tree.TreeLoader({    
        dataUrl:'carservice/Power!Powertree.action'   
        }),
        buttons:[{text:'选中的结果',handler:Oksubmit}] 
    });  

 怎么带参数到后台action 去？？？？？

在loader加baseParams

[code="js"]
var tree = new Tree.TreePanel({
el:'tree',
// region:'center',

useArrows:true,

autoScroll:true,
rootVisible:true,//是否显示根节点
animate:true,

enableDD:true,

containerScroll: true,

loader: new Tree.TreeLoader({

dataUrl:'carservice/Power!Powertree.action',
//参数
baseParams:{
method:'sayHello'
}
}),
buttons:[{text:'选中的结果',handler:Oksubmit}]
});

[/code]