4. The method of claim 1 further comprising: calculating a relevance value for at least one document for the terms assigned to leaf nodes of the tree structure; and presenting to a user as results of a search query at least one document resulting from the search query meeting a given relevance threshold value.
5. The method of claim 4 wherein the given relevance threshold value comprises at least one of: a minimum document relevance value; and a specified number of documents having highest respective relevance values to present to the user as the results of the search query.