1. A method for topic discovery through structural knowledge in an associative document tree building system, the method comprising: inserting a set of documents into nodes of a document tree in memory of a host computing system; extracting a tag set of tags from the set of documents and inserting each tag into a different node of a tag tree in the memory of the host computing system; conducting a search engine query through the host computing system using the tags of the extracted tag set to produce a new set of documents; inserting the new set of documents into nodes of the document tree; extracting a new tag set of tags from the new set of documents and inserting each of tag of the new tag set into a different node of the tag tree; and, displaying at least a portion of each of the document tree and tag tree in a user interface displayed by the host computing system.