org-odd-levels-only

org-odd-levels-only is a variable defined in `org.el'.
Its value is

nil

Documentation:
Non-nil means skip even levels and only use odd levels for the outline.
This has the effect that two stars are being added/taken away in
promotion/demotion commands. It also influences how levels are
handled by the exporters.
Changing it requires restart of `font-lock-mode' to become effective
for fontification also in regions already fontified.
You may also set this on a per-file basis by adding one of the following
lines to the buffer:

#+STARTUP: odd
#+STARTUP: oddeven

You can customize this variable.