parse_file doesn't do what you think it does. Instead it does what it says, it parses a file ;--). So HTML::TreeBuilder::XPath looks for a file named 'http://moneycentral.msn.com/investor/invsub/results/compare.asp?Page=TenYearSum' and doesn't find it, hence returning a quasi empty tree (the html, head and body elements).
You need to load the HTML yourself, for example by using LWP::Simple, and doing this:
