The song gently rippled on the waters of dusk In the twilight the factories were already glittering The train was speeding along The lights in the windows were brilliant The two young men under the hawthorn tree were looking forward to me When the loud whistle had just ceased I went along the path toward the tree The light wind blew ceaselessly Under the dense hawthorn tree The wind blew the hair of the young spinners and blacksmiths Ah, the dense hawthorn tree The white blossoms were full of flowers Our hawthorn tree ah Why is it sad

The song was sung by the young men of the factory, and they were singing in the evening. Why is the hawthorn tree sad?