I use ExtJS 4.1.3 an Architect.

This is my JSON:

{"success":true,"message":"Ricerca eseguita con successo","data":[{"text":"1) PIA CASA","expanded":false,"leaf":false,"iconCls":"ICON_D","children":[{"text":"1) REP.TULIPANO","expanded":false,"leaf":false,"iconCls":"ICON_D","children":[{"text":"1) spese del personale","expanded":false,"leaf":false,"iconCls":"ICON_D","children":[{"text":"1) direzione generale","expanded":false,"leaf":true,"iconCls":"ICON_D","children":null,"cdaCode":"01-01-01-01","cda1":null,"cda2":null,"cda3":null,"cda4":1},{"text":"3) ragioneria","expanded":false,"leaf":true,"iconCls":"ICON_D","children":null,"cdaCode":"01-01-01-03","cda1":null,"cda2":null,"cda3":null,"cda4":3}]}

Code:
Ext.define('myModel', {
    extend: 'Ext.data.Model',
    fields: [
    {name: 'text'},
    {name: 'expanded'},
    {name: 'leaf'},
    {name: 'iconCls'},
    {name: 'children'},
    {name: 'cdaCode'},
    {name: 'cda1'},        
    {name: 'cda2'},        
    {name: 'cda3'},        
    {name: 'cda4'}        
    ]
});     

Ext.create('Ext.data.TreeStore', {
		model: myModel,
		proxy: {
			type: 'ajax',
			api: MyApi,
			url: MyUrl,
			reader: {
				type: 'json',
				idProperty: '',
				messageProperty: 'message',
				root: 'data'
			}	
		}	
	});
When I load the store I see the tree, but when I click on the first item ("PIA CASA") I don't see its children but the tree is reloaded...

Immagine.png