A description is presented of a system, called approximate-tree-by-example (ATBE), which supports AI applications that involve comparing ordered labeled trees or retrieving/extracting information from repositories of such trees. The ATBE system interacts with users through a powerful query language; graphical devices are provide to facilitate inputting the queries. The system is designed to be extensible, customizable, and portable, which makes it a very useful tool for tree pattern matching in various environments. The use of the tool is illustrated. Several examples taken directly from the complete implementation are discussed.