This is normal with decal trees, as this is something you can’t just fix. But if you make a tree with just parts you won’t have this problem (Obviously).
If you were to search up a “Decal Tree” in the Model section they all act the exact same way just cause they are on a flat surface and are see through and to were the parts are thin.
There is no way to sadly avoid this with Decal Trees, this has been a problem since I became a developer and if you wish for this to not happen I would just say to make a actual tree. As there is no way to prevent this sadly. Sorry.