Trees randomly burst into flame, then re-ignite

A tree in the map randomly burst into flame, doing so twice. The first time it did so the fire disappeared a few seconds afterwards. The second time, however, the tree began to burn down. I poured water on the tree and then removed it to see what would happen. The trees burst into flame again. After pouring water on it a second time it stopped. No lava was anywhere near this place. My nexus's battery was at 5% when this happened, if that helps.