There are several sets of commands for expanding trees to show additional levels and collapsing them to show only the higher levels. These work in the same way as Windows Explorer™ and many other standard tree based applications:
The expand tree Buttons across the top of the screen allow you to select the degree of expansion from 1 level to 4 levels.
The Expand Groups button (g) will expand the tree to just the Function Level of each branch. Expand (n) levels allows you to choose the level of expansion.