How do I find the selected node in an ExtJS TreePanel?

var tree = Ext.create('Ext.tree.Panel', {
    store: store,
    renderTo: 'tree_el',
    height: 300,
    width: 250,
    title: 'ExtJS Tree PHP MySQL',
    tbar : [{
        text: 'get selected node',
        handler: function() {
            if (tree.getSelectionModel().hasSelection()) {
                var selectedNode = tree.getSelectionModel().getSelection();

                alert(selectedNode[0].data.text + ' was selected');
            } else {
                Ext.MessageBox.alert('No node selected!');
            }

        }

    }]

});