GeoExt 2.0.2 - Checkboxes in Layer Tree does not work!

I am trying to generate a customized layer tree using GeoExt 2.0.2 My code is as follows:

var store = Ext.create('Ext.data.TreeStore', {
            model: 'GeoExt.data.LayerTreeModel',
            root: {
                expanded: true,
                children: [
                    {
                        plugins: ['gx_baselayercontainer'],
                        expanded: true,
                        text: "Mappe di base"
                    },{
                        expanded: true,
                        text: 'Dati amministrativi', 
                        leaf: false,          
                        children: [
                        {
                         text: "Area progetto",
                         layer: "area_progetto",
                         nodeType: "gx_layer",
                         iconCls: 'area_progetto',
                         checked: true
                        },
                        {
                         text: "Comuni italiani",
                         layer: "comuni_italia",
                         nodeType: "gx_layer",
                         iconCls: 'comuni_italia',
                         checked: true
                        }
                       ]
                     },{
                        expanded: true,
                        text: 'Percorso Via Regina', 
                        leaf: false,          
                        children: [
                        {
                         text: "Tratte",
                         layer: "via_regina_tratte",
                         nodeType: "gx_layer",
                         iconCls: 'via_regina_tratte',
                         checked: true
                        }
                       ]
                  }
               ]
             }
        });

tree = Ext.create('GeoExt.tree.Panel', {
        border: true,
        region: "west",
        title: "Layers",
        width: 250,
        split: true,
        collapsible: true,
        collapseMode: "mini",
        autoScroll: true,
        rootVisible: false,
        lines: false,
        store: store
    });

My purpose here is to create multiple folders with the layers that I select and I want to assign different icons for each layer. This code created subnodes as I want, and I can assign a different icon for each layer in the tree, but the checkboxes are not working. Do you have any ideas or suggestions about why they are not working and how I can make them work?

NOTE: radio buttons for base layers are working

NOTE2: Setting the "store" as follows actually work for overlay layers, but in this case one big folder is created containing every layer except the base maps and I cannot create different folders and assign different icons for each layer.

   var store = Ext.create('Ext.data.TreeStore', {
        model: 'GeoExt.data.LayerTreeModel',
        root: {
            expanded: true,
            children: [
                {
                    plugins: ['gx_baselayercontainer'],
                    expanded: true,
                    text: "Base Maps"
                },{
                    plugins: [{
                        ptype: 'gx_overlaylayercontainer'
                    }],
                    expanded: true,
                    text: 'Overlay Layers'
                }
            ]
        }
    });

I really appreciate your help. Thank you!