1. A method of browsing a plurality of media items, at least one of said media items being associated with a plurality of tag values, each tag value having a level, the method comprising the steps of: (a) constructing a hierarchical tree structure having a root node and tag values arranged at nodes according to the levels of the tag values, such that any tag value on any branch of the tree structure from a first tag value is associated with a media item with which said first tag value is associated; (b) displaying at least a first portion of the constructed tree structure in a graphical user interface; (c) promoting, in response to a user input, a level of a second tag value in the displayed portion and, in response to the promoting step, for each node in the level of the second tag value: (i) removing, in response to said promoting step, at least one node in the tree structure descendant from the node; (ii) adding a child node for the second tag value to an ancestor node of the node, in a case where the ancestor node of the node does not have the child node for the second tag value; (iii) replacing the node with a replacement node; and (iv) for each node removed in response to the user input to promote the level of the second tag value, inspecting the removed node and executing at least one of the following steps to create a reconstructed tree structure: (iv-a) if a path from the removed node to the root node does not have a tag value in the level of the second tag value before the promotion, adding the removed node as a child node to the replacement node; and (iv-b) if the path from the removed node to the root node has a third tag value in the level of the second tag value before the promotion, such that the second tag value is associated with a media item with which said third tag value is associated, adding the removed node as a child node of the node with the second tag value, wherein the reconstructed tree structure is created such that associations of the plurality of tag values with the plurality of media items remain after the reconstructed tree structure is created; and the method further comprising: (d) displaying at least a second portion of the reconstructed tree structure in the graphical user interface.