Before handover - tree falls onto neighboring property

Regardless of law and moral views: If the current owner does not want to take care of it and the new owner insists, then payment and transfer will be delayed. This not only entails inconvenience but also a cost risk that far exceeds the tree removal costs.

Take a pragmatic approach, remind the seller of his statement that he wants to take care of it, offer to help him if he is overwhelmed, and be prepared to resolve the tree issue yourself if necessary.

You hand over your stuff properly, I think

That is certainly the case. If I had an apartment, I would hand it over broom-clean. But planting is now once on every "field". I also read tree row. Surely, as the seller, I probably haven’t even set foot on this property this year in a very unenthusiastic way... I also won’t plow weeds... I think the approach of sitting it out is understandable and others would do the same if they are honest. Mentally, the rights have already been assigned too.