How to handle 'real' TreePanel beforeload event?

[abent]

I want to make a logger TreePanel plugin for recording whether a tree node and its posterity is expanded,and while the node reloaded, it can help to rebuild structure.So I try to handle TreePanel's and TreeLoader's beforeload event,but can't get the node's structure.In ext-all.js:
Ext.tree.TreeLoader

    load : function(node, callback){
        if(this.clearOnLoad){
            while(node.firstChild){
                node.removeChild(node.firstChild);
            }
        }
        if(this.doPreload(node)){ 
            if(typeof callback == "function"){
                callback();
            }
        }else if(this.dataUrl||this.url){
            this.requestData(node, callback);
        }
    }
    requestData : function(node, callback){
        if(this.fireEvent("beforeload", this, node, callback) !== false){
            this.transId = Ext.Ajax.request({...... 

Before 'beforeload' event tigger,all children removed.I think the 'beforeload' event is not real 'beforeload' event,how to handle 'real' TreePanel beforeload event？