similar question:
is it possible to fix a tree in the part design for example that mouse scrolling does not move it by mistake (like it can be seen in the photo in the catia itself)
it can be quite annoying, i must say.
Try on the tree top to use "open sub tree" and hide (F3) the tree. It will open the tree in a separate window that I beleive will not be affected by indirecet mouse operations. I find it quite helpfull with dual screens to move the tree to the other window