@MagRiz, as @Tushar says, there is no easy way to do this, such as adding it to the QAT.....another way is to double click [any of] the stack header[s] to toggle between expand & collapse. The problem is, as you say, when the pathfinder is very long, the main stack header is part of the scrolling bundle.
The best way to combat this condition, would be to make use of pathfinder groups, such as seen in this video.
Design Manager Streetscape Ltd
Solid Edge ST10 [MP6] Classic [x2 seats]
Windows 10 - Quadro P2000
@MagRiz Not sure what the root issue is that you desire to regularly collapse the Pathfinder tree, but if it is to make it easier to find a component that was selected in the graphics window in a long Pathfinder tree, there is a Solid Edge Options setting in Assy under the Assembly section called "Auto-scroll assembly pathfinder" that will always cause it to scroll and expand to the selected component.