You can certainly make less elaborate ladders than the one shown here. This one used a hemlock handrail as rungs and two angled 2 x 3's as uprights. The rungs were attached to the uprights using countersunk 1/4" bolts (see photo). Longer bolts were used for the topmost rung to fix it to the bunkbed. I found the ladder easier to make in place, scribing all the bits I needed to cut. A vertical ladder would have been easier, for sure.