pstree visually merges identical branches by putting them in square brackets and prefixing them with the repetition count, e.g.
init-+-getty
|-getty
|-getty
`-getty
becomes
init---4*[getty]
Child threads of a process are found under the parent process and are shown with the process name in curly braces, e.g.
icecast2---13*[{icecast2}]
If pstree is called as pstree.x11 then it will prompt the user at the end of the line to press return and will not return until that has happened. This is useful for when pstree is run in a xterminal.