How can I add two or more layers in a group so that I can see them in layerswitcher categorised and can select or unselect all !?  

Here is the code I have:

```
            var line_1 = new OpenLayers.Layer.Vector(" Line no - 1", {
                    visibility: true,
                    projection: dproj,
                    strategies: [new OpenLayers.Strategy.Fixed()],
                    style: {strokeWidth: 4, strokeColor: "#ff0000", strokeOpacity: 1},
                    protocol: new OpenLayers.Protocol.HTTP({
                        url: "lines/en/line_1.kml",
                        format: new OpenLayers.Format.KML
                    })
            });

            var line_2 = new OpenLayers.Layer.Vector(" Line no - 2", {
                    visibility: true,
                    projection: dproj,
                    strategies: [new OpenLayers.Strategy.Fixed()],
                    style: {strokeWidth: 4, strokeColor: "#008000", strokeOpacity: 1},
                    protocol: new OpenLayers.Protocol.HTTP({
                        url: "lines/en/line_2.kml",
                        format: new OpenLayers.Format.KML
                    })
            });
 var layers = [line_1, line_2]
 map.addLayers(layers);

```

Now how can I gorup these two in 1 with the name "Lines" ?