1. An information processing device, comprising: estimation means for estimating, for a target category that is one of a plurality of categories which have a tree structure comprising a plurality of hierarchy levels and to each of which one or more objects belong, a user's degree of familiarity with categories below the target category, based on an input from the user; and display control means for controlling whether or not display means displays the categories below the target category, based on a result of estimation made by the estimation means.