Could a barrel be made with extremely large planks made from the entire length of a tree trunk? Let's say that the trees are about 20m tall. These barrels would be made by the fossorial people described in this question, and would be partially set into the ground as a silo. They might also use them (or smaller versions) to make things that couldn't be carved into soil
According to the Guinness world records
The largest wooden barrel measured 9 m (29 ft 7 in) tall, 9 m (29 ft 7 in) in diameter, and has a capacity of 540,000 litres (142,652.9 US gal). It was made by Fundokin Soy Co. Ltd. in Usuki City, Oita, Japan, in 2002. The barrel was made for brewing soy sauce.
Keep in mind that, out of a tree x meter high, the portion that you can use to make a plank is shorter than x, since the entire trunk cross section shrinks as the height increases.
10 meters plank out of a 20 meters high tree seems a good call.