New option --tree to output directory trees of files for options -l (--files-with-matches), -L (--files-without-match) and -c (--count). Updated option --pretty to enable --tree when output is sent to a terminal. Disable with --no-tree to output a traditional grep flat list.
For example, when pretty is specified in a .ugrep file, ug -l (--files-with-matches) outputs directories in a tree-like format similar to the unix tree utility: