Tree house
From Halopedia, the Halo wiki
The Tree House was a platform a 100 meters off the jungle floor on the planet Onyx, in the titan arms of a banyan tree. The only electronics it had were a radio and a AI projection unit, everything else was low-tech: optic binoculars and telescopes, parabolic sounds collection dishes, and "good old-fashioned" signal flags.
It was destroyed during the events of the Battle of Onyx.