Create a python program to display a histogram of the list items.
[1, 2, 3, 3, 3, 4, 4, 4, 4, 5, 6, 7, 8, 9]
import matplotlib.pyplot as plt

list_data = [1, 2, 3, 3, 3, 4, 4, 4, 4, 5, 6, 7, 8, 9] 
plt.hist(list_data, bins=6) 
plt.title("Histogram") 
plt.show()