A term analyzer receives an ordered collection of text-based terms. The term analyzer analyzes groupings of consecutive text-based terms in the ordered collection to identify occurrences of different combinations of text-based terms. In addition, the term analyzer maintains frequency information representing the occurrences of the different combinations of text-based terms in the collection. The frequency information can then be used to determine relatively significant keywords and/or keyword phrases in the document. In an example configuration, the term analyzer creates a tree in which a first term in a given grouping of the groupings is defined as a parent node in the tree and a second term in the given grouping is defined as a child node of the parent node in the tree. The method of the analyzer generalizes to create a tree of multi-word terms in which the terms can be efficiently ranked by occurrence.