You must do something wrong here, the following code works, see this JSFiddle
Ext.create('Ext.tree.Panel', {
collapsible: true,
title: 'Simple Tree',
width: 200,
height: 150,
store: store,
rootVisible: false,
renderTo: Ext.getBody(),
listeners: {
collapse: function() {
alert('collapsed');
},
expand: function() {
alert('expand')
}
}
});