My first iquestion is if the ClientID you're passing to the $find method is actually the RadTreeView control's or some other control? From your example it looks like you might be passing in the wrong id. Also, when are you calling this code? If it's during the page load I would suggest using the following approach:
tree = $find(
"<%= uclPanelTabReport1.ClientID %>"
The reason for calling it this during the pageLoad is because the RadTreeView client object isn't initialized during the normal js load event.
To answer you question about the $("#RadTreeView.ClientID") call, it does not retrieve the correct reference to the RadTreeView thus the reason FireBug would say trackChanges isn't a method of the RadTreeView.
I hope that helps.