In ps xf
26395 pts/78 Ss 0:00 \_ bash 27016 pts/78 Sl+ 0:04 | \_ unicorn_rails master -c config/unicorn.rb 27042 pts/78 Sl+ 0:00 | \_ unicorn_rails worker[0] -c config/unicorn.rb In htop, it shows up like: 
Why does htop show more process than ps?
By default, htop lists each thread of a process separately, while ps doesn't. To turn off the display of threads, press H, or use the "Setup / Display options" menu, "Hide userland threads". This puts the following line in your ~/.htoprc or ~/.config/htop/htoprc (you can alternatively put it there manually):
hide_userland_threads=1 (Also hide_kernel_threads=1, toggled by pressing K, but it's 1 by default.)
Another useful option is “Display threads in a different color” in the same menu (highlight_threads=1 in .htoprc), which causes threads to be shown in a different color (green in the default theme).
In the first line of the htop display, there's a line like “Tasks: 377, 842 thr, 161 kthr; 2 running”. This shows the total number of processes, userland threads, kernel threads, and threads in a runnable state. The numbers don't change when you filter the display, but the indications “thr” and “kthr” disappear when you turn off the inclusion of user/kernel threads respectively.
When you see multiple processes that have all characteristics in common except the PID and CPU-related fields (NIce value, CPU%, TIME+, ...), it's highly likely that they're threads in the same process.
For me, on a more-or-less current arch linux system, ps xf shows me only the processes owned by my user ID. htop shows me all processes. Try ps -ef for a list of all processes, or perhaps ps -ejH to get a child/parent relationship listing.
htop. htop is also showing processes that have ended. This is great, so you can see short-lived processes and what resources they might have consumed. If you exit htop and restart it, you'll see they have disappeared. I can't figure out a way to make htop drop historical processes without restarting, so maybe there's a way.
