One problem with being up a tree is not being able to get back down in a hurry. Nor was it wise to surrender the freedom of movement on the battlefield.

This suggests the photos were taken well before any combat in New Guinea.

By the final year of the war, the troopers received - and preferred - the standard green HBT's, and the use of the camouflage uniform became uncommon.  There were none on Corregidor.