Bunk bed designs come in many different forms. There are I-shaped bunk beds with aligned upper and lower levels. There are L-shaped beds with different orientations on the upper and lower levels. There are also asymmetrical styles, with single beds on the upper floor and double beds on the bottom.
The orientation is mainly limited to the layout of the bedroom. In general, the designer will consider the direction and position of the door opening and closing, the position of the air-conditioning, the lighting of the window, and whether the wall is restricted by beams and columns. All of this info is used to determine the placement and direction of the bunk bed.
If one of the walls has a column sticking out, then the long side will not be placed there.
The A/C unit should not be blowing directly on the bed, which could make the person sick or cause sleep issues.
You also want to avoid blocking too much of the natural light with the bed frame.