In this excerpt from "The Legend of Sleepy Hollow,” what is the foreshadowing?

Question

It [the tree] was connected with the tragical story of the unfortunate André, who had been taken prisoner hard by; and was universally known by the name of Major André's tree. The common people regarded it with a mixture of respect and superstition, partly out of sympathy for the fate of its ill-starred namesake, and partly from the tales of strange sights and doleful lamentations told concerning it.
As Ichabod approached this fearful tree, he began to whistle; he thought his whistle was answered–it was but a blast sweeping sharply through the dry branches. As he approached a little nearer, he thought he saw something white, hanging in the midst of the tree–he paused and ceased whistling; but on looking more narrowly, perceived that it was a place where the tree had been scathed by lightning, and the white wood laid bare. Suddenly he heard a groan–his teeth chattered and his knees smote against the saddle: it was but the rubbing of one huge bough upon another, as they were swayed about by the breeze.

Answer 1

Ichabod thought he saw a ghost. How does that tie in with later events in the story?