Hi XP Investimentos,
That's a tough one, unfortunately for the time being we are not offering this functionality with our Navigation control. Thank you for pointing out the need for its implementation, though. In case of future revision of the Navigation control we'll surely address this issue.
A possible workaround, although not the perfect solution, is to place a second Navigation control on the page which you want the node to be expanded and specify it to display all pages under the parent node in expanded state. Although this will deliver the desired functionality, I'm not sure if you will find it appropriate design-wise, but you can still try.
If you need any further assistance with this, please write back.
the Telerik team