Code
<script language="JavaScript" type="text/javascript">
    <!--
    Ext.BLANK_IMAGE_URL = '../resources/ext/resources/images/default/s.gif';

Ext.onReady(function() {
        var ddTree = new Ext.tree.TreePanel({
            el: 'ddTree',
            useArrows: true,
            enableDD: true,
            width: 200,
            height: 300,
            loader: new Ext.tree.TreeLoader({
                dataUrl: "xxx.ashx"
            }),
            rootVisible: false,
            root: new Ext.tree.AsyncTreeNode({}),
            listeners: {
                'beforeload': beforeloadHandler,
                'load': loadHandler
            }
        });

ddTree.render();
        ddTree.expandAll(); // 展开所有结点

　　   var loading = null;
        function beforeloadHandler() { // 加载前事件响应处理
            loading = new Ext.LoadMask(Ext.get(ddTree.getEl()), { msg: "请等待" });
            loading.show();
        }

function loadHandler() { // 加载后事件响应处理
            loading.hide();
        }
    });
    -->
    </script>

Code
<script language="JavaScript" type="text/javascript">
    <!--
    Ext.BLANK_IMAGE_URL = '../js/ext/images/default/s.gif';

Ext.onReady(function() {
        var forumTree = new Ext.tree.TreePanel( {
            el: 'forumtree',
            useArrows: true,
            enableDD: true,
            width: 200,
            height: 300,
            rootVisible: false,
            root: new Ext.tree.AsyncTreeNode({})
        });
        
        forumTree.render();
        
        // 加载提示
        var loading = null;
                
        function showLoading() {
            loading = new Ext.LoadMask(Ext.get(forumTree.getEl()), { msg: "请等待" });
            loading.show();
        }

function hideLoading() {
            loading.hide();
        }
        
        showLoading();
        
        // 由于使用TreeLoader在IE下无法正常加载数据,所以使用Ajax先获取数据再填充数据到root node下 
        Ext.Ajax.request({
            url: 'xxx.ashx',
            success: function(request) {
                var data = Ext.util.JSON.decode(request.responseText);
                forumTree.getRootNode().appendChild(data);
                forumTree.getRootNode().expandChildNodes(true);
                
                hideLoading();
            },
            failure: function() {
                hideLoading();
                
                Ext.MessageBox.show({
                    title: '版块管理',
                    msg: '对不起,加载数据出现异常,请重试!',
                    buttons: Ext.MessageBox.OK,
                    icon: Ext.MessageBox.ERROR
                });
            }
        });
    });
    -->
    </script>

Code
function removeChildNodes(node) {
            while(node.firstChild) {
                removeChildNodes(node.firstChild);
            }
  
            if(node.getDepth() != "0") {
                node.remove();
            }
        }