People regarded Major Andre's tree with superstition because André was taken prisoner by it.
Major John Andre, a British spy, in collaboration with the notorious American traitor Benedict Arnold, was attempting to deliver documents from Arnold that would have compromised the security of the U.S. fort at West Point.
With the documents hidden in his socks, Andre was travelling through Sleepy Hollow and Tarrytown, enroute to British-controlled territory to the south. By chance, he was detained by three local militiamen on watch that morning, who discovered the documents and took him into custody.
Ultimately, this led to Andre's execution, and forced Benedict Arnold to hastily defect to Britain in order to avoid a similar fate.
In the “Legend of Sleepy Hollow”, the tree has been extensively described as follows:
Many dismal tales were told about funeral trains, and mourning cries and wailings heard and seen about the great tree where the unfortunate André was taken, and which stood in the neighborhood. Some mention was made also of the woman in white, that haunted the dark glen at Raven Rock, and was often heard to shriek on winter nights before a storm, having perished there in the snow. The chief part of the stories, however, turned upon the favorite spectre of Sleepy Hollow, the Headless Horseman, who had been heard several times of late, patrolling the country; and, it was said, tethered his horse nightly among the graves in the churchyard.