Groundhogs can climb trees.
Although in the past, I've seen a groundhog up a small tree to escape danger https://pbase.com/britestar/image/78475053,
the above scene certainly made me do a double take. Maude's pup scaled our Bradford Pear with ease!!!

Why did she do it?
Just because she could.

For no apparent reason, Lumpy went up the tree (much higher than this) & then immediately came down. Then, she went up again, and came down again. When I first saw her, I just stared with my mouth open in amazement. This is not a little tree. How did she do it??? Her vertical climbing form was certainly different. I grabbed my nearby camera as fast as I could, but she had come down for the second time before I could do anything. BUT then, she went up again for the third time, & then, came right back down again. This gave me the chance to take at least one photo of the action. After that, she ran to catch up to her waiting litter mate with whom she seems to be very bonded. They then disappeared out-of-sight into our front yard.

This is the smallest of Maude's 4 pups. She's only half the size of her best buddy, litter mate. We call her "Lumpy". She always seems to be investigating something.