FreeBSD psコマンドでプロセスの親子関係を表示する方法

% ps ad
  PID  TT  STAT      TIME COMMAND
  953  v0  Is+    0:00.01 /usr/libexec/getty Pc ttyv0
  954  v1  Is+    0:00.01 /usr/libexec/getty Pc ttyv1
  955  v2  Is+    0:00.01 /usr/libexec/getty Pc ttyv2
  956  v3  Is+    0:00.01 /usr/libexec/getty Pc ttyv3
  957  v4  Is+    0:00.01 /usr/libexec/getty Pc ttyv4
  958  v5  Is+    0:00.01 /usr/libexec/getty Pc ttyv5
  959  v6  Is+    0:00.01 /usr/libexec/getty Pc ttyv6
  960  v7  Is+    0:00.01 /usr/libexec/getty Pc ttyv7
  975   0  Is     0:00.26 -csh (csh)
10884   0  I+     0:00.23 - make WITH_PYTHON=yes WITH_RUBY=yes WITHOUT_X11=yes install clean
17723   0  I+     0:00.01 `-- [sh]
17732   0  I+     0:00.10   `-- make -DINSTALLS_DEPENDS install PYTHON_VERSION=python2.6 RUBY_VER=1.8
17748   0  I+     0:00.14     `-- make CONFIG_DONE_RUBY=1 /usr/ports/lang/ruby18/work/.install_done.ruby._usr_local
17829   0  I+     0:00.01       `-- [sh]
17918   0  I+     0:00.09         `-- make -DINSTALLS_DEPENDS install RUBY_VER=1.8
17946   0  I+     0:00.01           `-- [sh]
17955   0  I+     0:00.12             `-- make -DINSTALLS_DEPENDS install
17974   0  I+     0:00.16               `-- make CONFIG_DONE_PERL=1 /usr/ports/lang/perl5.8/work/.install_done.perl._usr_local
23190   0  I+     0:00.01                 `-- [sh]
23191   0  S+     0:00.07                   `-- make -f Makefile all
25702   0  S+     0:00.02                     `-- sh ext/util/make_ext dynamic lib/auto/NDBM_File/NDBM_File.so MAKE=make LIBPERL_A=libperl.so
25712   0  R+     0:00.04                       `-- ../../miniperl -I../../lib Makefile.PL INSTALLDIRS=perl INSTALLMAN3DIR=none PERL_CORE=1 LIBPERL_A=libperl.
23952   1  Is     0:00.15 -csh (csh)
24072   1  S+     0:00.03 - screen
24075   2  Ss     0:00.20 /bin/csh
25713   2  R+     0:00.00 - ps ad