I have a tree in my application(ExtJs 3.4), how I can add a filter?

My code:

var treeLoader = new Ext.tree.TreeLoader({
            dataUrl: this.entrypoint, 
            baseParams: {m:this.modName,a:'get-nodes'}

        var clientiRootNode = new Ext.tree.AsyncTreeNode({id: 'clienti-root'});
        this.treePanel = new Ext.tree.TreePanel({
            loader: treeLoader,
            autoScroll: true,
            animate: true,
            autoScroll: true,
            border: false,
            // enableDD: true,
            root: clientiRootNode,
            selModel: new Ext.tree.DefaultSelectionModel(), 
            lines: false, 
            rootVisible: false, 

            // tbar: tbar, //NOTA: se aggiungo la toolbar, quando nascondo il tree panel, il nodo root perde i nodi figlio
            listeners: {
                beforeexpand: function(p){p.getRootNode().expand();} 
Ps: the tree is like a list, there are no nodes with deep more than "one"...