I was quite surprised when I saw these videos the first time and then read the lyrics from The Jungle Book movie, just how good a fit they are. There definitely seems to be some form of enjoyment going on. Its a bit like a life lesson for us all - simple pleasures are usually the best...
But the probable reality is that these males are using the tree, and the same trees repeatedly, to scent mark. It is believed they do this as a form of communication between males so that they "know" other males sharing overlapping areas. Work on Grizzly bears by Owen Nevin of the University of Cumbria in 2007 concluded:
".... cameras show that adult male bears are the most likely to rub trees, and the satellite telemetry tells us that males move from valley to valley in large loops, marking trees as they go, while looking for breeding females,"
Nevin thinks that by marking the trees with their scent, the male bears get to "know" each other better, which may reduce fighting among the bears over potential female mates.
"...male bears can seriously injure or even kill each other when they get into a fight," Nevin said. "If one recognizes the other from the scent marks on the rub trees in the area, he knows he's in for a tough fight—he's on the other guy's patch so to speak—so it might be better to back away than make a serious challenge."
There are clearly at least two males, possibly three, in the video and they visited the same tree repeatedly over a 6 week time frame in the Dong Phayayen - Khao Yai World Heritage site. We also have accidental footage of them using the tree before this but this camera was placed specifically to see if we could possibly catch this behaviour closely on video. A successful attempt I think.