I also faced the same problem. They are tracing lines inside my bidurcation diagram. I found this solution.

Here is my code.

import matplotlib.pyplot as plt
import numpy as np

def logistic(x, a):
    return a * x * (1 - x)

# Range of 'a' values
k = np.linspace(2.8, 4, 1000)

# Number of iterations and data collection after transients
n = 200
m = 50  # Collect the last 50 points to visualize bifurcation

x_axis = []
y_axis = []

for a in k:
    x0 = 0.1  # Initial value of x
    # Iterate to remove transient behavior
    for i in range(n):
        x0 = logistic(x0, a)
    # Collect data for plotting bifurcation
    for i in range(m):
        x0 = logistic(x0, a)
        x_axis.append(a)
        y_axis.append(x0)

# Plotting the bifurcation diagram
plt.figure(figsize=(10, 7))
plt.plot(x_axis, y_axis, ',k', alpha=0.25)  # Small markers for clarity
plt.title("Bifurcation Diagram")
plt.xlabel("Parameter a")
plt.ylabel("Population")
plt.show()

But the problem here why is it loop until 100 at the first loop and then continue the iteration?