Class 'clt\leftnav' not found

//        }
        $adList=[];
        $this->assign('adList', $adList);
        // 获取缓存数据
        $cate = cache('cate');
        if(!$cate){

            $column_one = Db::name('category')->where([['pid','=',0],['ismenu','=',1]])->order('sort')->select();
            $column_two = Db::name('category')->where('ismenu',1)->order('sort')->select();
            $tree = new  \clt\leftnav();
            $cate = $tree->index_top($column_one,$column_two);
            cache('cate', $cate, 3600);
        }
        $this->assign('category',$cate);

    }