You question is some what not complete. For starters you need to explain what you mean by 'HTML Trees'. The fact that you put it in quotes suggest that you meant something, but clearly you know that is not the term. Also, the fact that you are unable to find any good hits with google may be the use of incorrect terms.
By 'HTML Trees', I am assuming you are talking about the html structure, right? something like
Is that what you have in mind? If not then there is no point in continuing. But if we are in agreement, well, depending when shallow or somewhat deep you work/project/assignment is the best source is to learn something about HTML specification. You don't need to go deep, just enough to get you going and solve your problem. I understand you are not trying to create the next killer
Browser. Here is good starting point http://www.w3.org/html/
Next there are few C++ HTML parsers around. You will be able to better understand what is going on if you have some understanding of the HTML spec. Then when you ready check
HTML Reader C++ Class Library
and of course our old friend recommends this