For a thorough discussion of the chart of account rules, see the Chart of Accounts Setup topic > Chart of Account Rules section.

Group Level Restrictions	Group level 1 accounts cannot be added. The account immediately preceding a level 1 group account must be a detail account. A group account cannot be higher than a level 4. A group account immediately following another group account, must descend a level. A group account that follows a detail account cannot descend a level.
Adding Group Accounts	Group accounts can be added with a level higher than the preceding group account. Group accounts can be added with a level equal to the preceding group account. Group accounts can be added with a level lower than the preceding group account.
Adding Detail Accounts	A detail account that immediately follows a group account must descend one level. A detail account that immediately follows a detail account cannot descend a level.