Half autumn

This tree has two trunks. Half of the tree believes it is autumn and hence the leaves are not green anymore. The other half of the tree still thinks it is summer, all leaves are still green. Also the number of leaves is accordingly.
I have no idea why this is. The sun comes mostly from this side, the wind also. So same condition for both trunks. Perhaps it is something in the part where both trunks are still one.