1. A computer-implemented method comprising steps of: receiving a set of user-specified criteria; adding to a tree structure, a first set of two or more nodes that are determined based at least in part on the user-specified criteria; associating, with each node in the first set, a separate set of criteria that are based at least in part on the user-specified criteria; displaying the tree structure to which the nodes in the first set have been added; receiving user input that indicates selection of a particular node from the first set; in response to receiving the user input, determining one or more records that satisfy the set of criteria that is associated with the particular node; adding, to the tree structure, a second set of nodes that are generated based at least in part on the one or more records; and displaying the tree structure to which the nodes in the second set have been added; wherein the user-specified criteria specifies a column in a relational database table; and wherein adding the first set of nodes to the tree structure comprises adding, to the tree structure, for each unique value that occurs in the column of the relational database table, only one node for said unique value; wherein the column includes multiple instances of at least one unique value that occurs in the column; wherein the steps are performed by one or more computing devices.