This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
I assume you know how to read all entries in a Zip file.
I would keep a mapping from entry names to DefaultMutableTreeNodes. Then, when you encounter a ZipEntry, you determine its parent from the name (using the / as the separator*). You retrieve the parent node from the map, creating it if necessary. Then you create a DefaultMutableTreeNode, and add it to the parent node. Finally you add the new mapping.