I just switched to the new snapshot 25w04a. I planted a few oak saplings, and then I noticed it. The two seedlings were not standing side by side, but the tree grew like this. And this is not one such tree.
To reproduce the bug, it is enough just to plant a lot of seedlings. Some tree will grow like this.
P.S. - I planted more oak saplings and again these strange trees!
P.S. 2 - I play with my friends, that is, in multiplayer. This server was created using Aternos. There were no such trees before, but as soon as I switched to this version, such errors started immediately.