tree [-d] [directory...]
-d Display only the directories.
-h Usage information
-v Version information
$ tree ~/man
/home/joppa/horton/man
man1
glcheck.1
glunpack.1
xviewgl.1
pstext.1
mif2troff.1
recent.1
bigfiles.1
netconfig.1
prog2mif.1
gs.1
man3
Sprint.3
sio.3
strparse.3
strprint.3
strs.3
strutil.3
MANPATH=$MANPATH:/home/joppa/horton/man
Only regular files are considered.