System monitor can do all this stuff, pstree and all, and you can get really cool visualizations. Pi charts, line graphs, and my personal favorite, color grid. That one's really good for CPU utilization.
But the real icing is that it doesn't just work for processes, applications, CPU usage and whatnot. It works for any sensor, including temperature and fans. And, of course, it's all customizable.
Be that as it may, it is slow to start, or switch between different views. I tested that again just now. Furthermore, it's causing more load by running, than one btop++ or htop running in Konsole. Which btw. both show temperatures, and could also show the rpm of the little 'Miefquirl'...err.. fan if I wanted them to.
That's seems to be common for all the monitoring stuff running graphically, no matter if Gnome, XFCE, or even old KDE (Trinity).
That aside, htop and especially btop++ are heavily customizable, too.
Whatever. To each his own. It's a matter of taste.
Yeah it's pretty fast but it's still a full graphical application. It's probably written using QtQuick so it's fast... ish. Terminal applications are almost always going to be much faster. But, it's a neat application that doesn't get much competition on the GUI side.
But the real icing is that it doesn't just work for processes, applications, CPU usage and whatnot. It works for any sensor, including temperature and fans. And, of course, it's all customizable.