Yes tree climbing robots are a reality. It was developed by studying how animals are able to climb vertical surfaces.
“The goal of the RiSE project is to create a bioinspired climbing robot with the unique ability to walk on land and climb on vertical surfaces. Active research studies novel robot kinematics, precision-manufactured compliant feet and appendages, and advanced robot behaviors. This project is funded by the DARPA Biodynotics Program.”
Here is what makes it tick:
The RiSE platform runs QNX 6.1.0 on a Geode 266MHz processor. The body (v1.0) contains 12 Maxon RE motors and a 4-bar linkage connected through a differential (v1.2 uses a belt drive system) that reveals 2 DOF (wing and crank angle) per leg. The leg position is controlled by RMCs (RiSE motor controller) that use PD control. Currently the body uses LSANs (leg sensing and actuation node) to collect sensor info (accelerometer, potentiometer on 4-bar joint) for feedback. Generarally, BDI designed the robot hardware, CMU devloped the software by CMU, and Stanford is devlopming the feet and some related sensing.