jsTree and Context Menu: modify items

I'm using jsTree 3.0.0 and I need to modify the context in one of the following ways:

• Change label language for the default items, disable some default items and add new items.
• Rewrite all items and bind to some new items the create, rename and delete function.

I tried several approaches but nothing worked. For example, this returns Uncaught TypeError: Object [object global] has no method 'create' when I click on create.

"contextmenu":{
    "items": function($node) {
        return {
            createItem : {
                 "label" : "Create New Branch",
                 "action" : function(obj) { this.create(obj); alert(obj.text())},
                 "_class" : "class"
            },
            renameItem : {
                 "label" : "Rename Branch",
                 "action" : function(obj) { this.rename(obj);}
            },
            deleteItem : {
                 "label" : "Remove Branch",
                 "action" : function(obj) { this.remove(obj); }
            }
        };
    }
},

If I try to add one item as in the next example, I loose the default menu items:

items : { 
    "create_folder" : {
        "separator_before" : false,
        "separator_after" : false,
        "label" : "Create Folder",
        "action" : function (obj) { alert(1); /* this is the tree, obj is the node */ }
    }
}

Where am I wrong?

Resolved:

"contextmenu":{         
    "items": function($node) {
        var tree = $("#tree").jstree(true);
        return {
            "Create": {
                "separator_before": false,
                "separator_after": false,
                "label": "Create",
                "action": function (obj) { 
                    $node = tree.create_node($node);
                    tree.edit($node);
                }
            },
            "Rename": {
                "separator_before": false,
                "separator_after": false,
                "label": "Rename",
                "action": function (obj) { 
                    tree.edit($node);
                }
            },                         
            "Remove": {
                "separator_before": false,
                "separator_after": false,
                "label": "Remove",
                "action": function (obj) { 
                    tree.delete_node($node);
                }
            }
        };
    }
}