I would suggested Section 11.16 Listed Table Format. You will have to adapt the provisions given to allow for the number of levels. The second row heading shown, for instance, would be a very long cell-5 heading under the first column heading Content Descriptions. You can block the bulleted items in cell 7 and then proceed to the second column. The second column could be done as a nested list with the appropriate runovers, since is goes to 3 levels.
Follow the same given the in Formats and be sure to adapt it to the number of levels in this situation. You will not be able to follow the guidelines exactly as given for runovers. That's why these are called guidelines. They are to be adapted to the situation you have.
The only other suggested I could make would be to use facing pages (Sec. 11.13).