Its three way triangular shape which makes it very impressive. Once you mastered the technique, trinity knot is quite easy to tie.
NOTE:
It is suggested to use a tie that is either patterned or has small stripes, like the tie pictured. Do not use a tie with several different colored stripes, as the stripes and colors will collide in the knot.
Source here, here is the video tutorial if you wanna follow the instructions directly.