As mubed kindly pointed out, the tag palette is not very comfortable for browsing a large or deep tag tree. So in this version, I added a new pop-up view which allows you to browse a tag tree (and other types of view) more comfortably and intuitively.
Clicking on the tool button in the tag palette header opens the tags popup view:
This view also has a format switch: tree, cloud, flat:
You can download the latest release of Piggydb from: https://sourceforge.net/projects/piggydb/files/latest/download