Hmmm. . The only way that I can think of would be to make a sub-assembly. Create a separate assembly and place all those parts into it, then you would still have to apply all your constraints there, and then place that assembly into a larger assembly and it would display in the tree the way you want it to, but you would have to make any edits to that sub-assembly in its own file, not the larger assembly. So doing that has it's pros & cons. For what appears to be a set of stairs, it would probably work out ok, you're not going to drive any of those constraints or anything like that, they are just stairs sitting there. You can assemble the individual steps to the sides how you want them, call that assembly something like "staircase assy" or whatever you want, then when you put it in your larger assembly instead of having stair 1 stair 2 etc. in the tree, you'll have the "stair assembly" and move on. Hope this helps.