Article: Lay one of the treads you cut on the floor between the side rails. Then, mark its height on the side rails to help center your pilot holes. Move the tread out of the way after making the markings. The bottom rail rests on the ground in order to provide structural support. Create 2 pilot holes per side through the rails with a drill bit that is slightly thinner than the 2.5 in (6.4 cm) screws you’ll use here. Put the tread back into position on the floor and drive the 4 screws through the pilot holes and into the tread. Use a counter-sink drill bit for the pilot holes if you want to completely conceal the screw heads later. Along each side rail, measure the distance from the top of the bottom tread to the top of the upper bunk’s bed deck. Divide this measurement by 6 (for the remaining treads) and use this result to mark the location for each tread along both rails.  For instance, if the measured distance is 66 inches (170 cm), the centered markings for each tread will be 11 inches (28 cm) apart. If you have a taller than normal bed, you may need more than 6 additional treads. Working from the top-down or bottom-up, hold a cut tread centered between a set of the spacing positions you just marked. Use a spirit level (bar level) to make sure the tread is level both width- and depth-wise. Mark its top and bottom positioning against the inside of both side rails. Using your markings for guidance, drill pilot holes — 2 per side per tread — through the side rails. Then, using a level as your work to confirm the positioning, secure each tread to the rails with 2.5 in (6.4 cm) wood screws.  Recruit a friend to make this easier! While you can debate whether this is a ladder or a staircase, its angled rails and flat treads may be easier for kids to navigate than a vertical bed ladder.

What is a summary?
Position the bottom tread at the base of the side rails. Drill pilot holes and attach the bottom rail. Mark the spacing for the remaining treads on the side rails. Mark the leveled position for each tread on the side rails. Drill pilot holes and screw the remaining treads in place.