Hi Sergio,
Thanks for using syncfusion products.
We suggest you to use the following code to achieve your requirement.
[Javascript]
Sys.Application.add_load(function () {
$('#accordion-name').accordion({
active: false
});
});
Also I have created a simple sample and attached in the below link,
TreeView467840173.zipPlease try this and let us know if this helps.
Regards,
Vignesh