Drawing a fractal tree using turtle in python program

 import turtle
MINIMUM_BRANCH_LENGTH = 15
def build_tree(t, branch_length, shorten_by, angle):
  if branch_length > MINIMUM_BRANCH_LENGTH:
    t.forward(branch_length)
    new_length = branch_length - shorten_by
    t.left(angle)
    build_tree(t, new_length, shorten_by, angle)
    t.right(angle * 2)
    build_tree(t, new_length, shorten_by, angle)
    t.left(angle)
    t.backward(branch_length)
tree = turtle.Turtle()
tree.hideturtle()
tree.setheading(90)
tree.color('red')
build_tree(tree, 50, 5, 30)
turtle.mainloop()

Biopython - Python Tools for Computational Molecular Biology

Biopython is a set of freely available tools for biological computation written in Python by an international team of developers.