How would you go about mounting this to a wall? - whilst keeping mounting panels discreet
Steel bracket that then attaches to the bookshelf with some kind of hook hidden inside two of the vertical parts?
How big is the shelf? Without anything showing scale its hard to say what would work.
Draw pencil lines with a straight edge where your verticals are going to sit.
Mark the points where the intersections between the verticals and horizontals will be located.
Drill and insert wall plugs into the wall at the points where the intersections are.
Drill and countersink holes through the verticals at the same point. and attach them to the wall using a counter sunk screw and long driver extension or very long screwdriver.
Push the horizontals onto the verticals. If your tolerance is right, you shouldn’t need any adhesive, but if you do, be careful what you use because of runoff. Also if your glue is too strong, you’ll need to break the unit to remove it.
Also, come to think of it, you may want to drill your holes first, have someone assist you, and mark the wall with a pen/pencil through the holes to make it more accurate.
Although I when I bought a set at Uni (a fair few years ago) I’m sure there was a bracket you fixed to the wall with two protruding lengths of tube that aligned with blind holes in the shelf itself.
Edit. aka like this: