Nobody knows for sure how this happened; probably some bird dropped a seed on top of the mulberry which then grew roots through the hollow trunk of the host tree to reach the soil. While trees growing parasitically over another tree is not unusual, but they normally do not reach the size and lifespan as seen in this particular example, as there is not enough humus and space available where they grow. Large “double-trees”, also called Epiphytes, like the Bialbero de Casorzo are a rarity.
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