This panel is very similar to PacksPanel, but instead of simple list of available packs, the tree-like list is constructed. By using the parent attribute of packelement, one can specify the hierarchy of the tree. This panel supports grouping just like PacksPanel does.
The result tree contains a Base pack element with no children, and themes with two children named Black and Red.
The TreePacksPanel optionally deals with information about preinstalled packs during updates saved in $INSTALL_PATH/.installationinformation, see the <writeinstallationinformation> tag in Header - <info> section for more information.