The xps program displays and continuously updates in an X Window the Unix processes as a tree or forest.
Different users can appear as different colors too.
Within this, processes are arranged by userid with lower number uid's appearing towards the top. In general, the order of children is the order in which they were spawned, with the older processes appearing towards towards the top. A goal of the program is to visually give a picture of what's going on. So when possible processes are kept close to their parents so one needn't scroll around too much and so that there isn't a lot of redrawing as processes are created or destroyed. Since programs of this ilk can consume a bit of CPU on their own, some effort has been made to turn off the update process when the program is iconified or or not visible.