How to explain the weeping blood of Toona sinensis branches for three years?

Describe a person's grief to the extreme, tears like blood, wailing like a song, difficult to extricate themselves.

Creative background:

The poems of Su Shi and Huang Tingjian pushed the development of Song poetry to a peak, reflecting the characteristics of a generation. The "Jiangxi School", led by Huang Tingjian and others, advocates "turning stone into gold" and "taking fetus as bone", but ignores the poet's thoughts and feelings and his observation, experience and accumulation of life. Under this historical background, Yang Wanli's "Chengzhai Style" poetry, as a revision of Jiangxi Poetry School, has positive significance. This poem is a typical "sincere style" work.