[miha-ha]

У меня так работает:

var config = {
            readOnly: false,
            isExpand: false,
            mode: 'local',
            treeFilter:  new Ext.tree.TreeFilter(this.getTree(), {
                autoClear: true,
                filterBy : function(fn, scope, startNode){
                    startNode = startNode || this.tree.root;
                    if(this.autoClear){
                        this.clear();
                    }
                    var found = {};
                    var af = this.filtered, rv = this.reverse;
                
                    var f = function(n){
                        if(n == startNode){
                            return true;
                        }
                        if(af[n.id]){
                            return false;
                        }
                        var m = fn.call(scope || n, n);
                        if(!m || rv){
                            af[n.id] = n;
                            //                        n.ui.hide();
                            //                        return false;
                            return true;
                        }
                    
                        found[n.id] = n;
                        return true;
                    };
                
                    startNode.cascade(f);
                
                    for(var idf in found){
                        if(typeof idf != "function"){
                            var curFoundItem = found[idf];
                            var p = curFoundItem.parentNode;
                            while(p){
                                delete af[p.id];
                                p = p.parentNode;
                            }
                        }
                    }
                
                    for(var id in af){
                        if(typeof id != "function"){
                            var n = af[id];
                            n.ui.hide();
                        }
                    }
                
                    //startNode.cascade(f2);
                
                    if(this.remove){
                        for(var id in af){
                            if(typeof id != "function"){
                                var n = af[id];
                                if(n && n.parentNode){
                                    n.parentNode.removeChild(n);
                                }
                            }
                        }
                    }
                }
            }),

            listeners: {
                scope: this,
                beforequery: function(){
                  return false;
                },
                keyup: {
                    fn: function(field, key){
                        if(!this.isExpand)
                            this.expand();
                        var value = field.getRawValue();
                        if(Ext.isEmpty(value) && !Ext.isEmpty(field.treeFilter)){
                            field.treeFilter.clear();
                            return;
                        }
                        var re = new RegExp('' + value + '', 'i');
                        var tree = field.getTree();
                        tree.expandAll();
                        field.treeFilter.filter(re);
                    },
                    buffer: 250
                }
            }
        }