After toying around a bit with custom terrain and biome generation, I've came around a weird bug where all trees spawn in a grid formation, There was a similar issue with birch trees in 20w28a but this has been solved. saddly it still occurs to trees when you use them in custom generation. To reproduce, use on of the tree configured_feature's when creating a custom biome, and all of them will spawn in this grid formation, this also applies to jungle bushes.