<｜begin▁of▁sentence｜>### Instruction:
Given a directed tree with edge set [(0, 1), (0, 2), (1, 3), (1, 4), (2, 5), (2, 6)], how can the Reingold-Tilford layout algorithm be used to visualize the tree in a hierarchically structured manner using igraph?
### Response:
from igraph import Graph
import matplotlib.pyplot as plt

# Define the edges for a sample tree
edges = [(0, 1), (0, 2), (1, 3), (1, 4), (2, 5), (2, 6)]

# Create a tree with the defined edges
tree = Graph(edges=edges, directed=True)

# Calculate the layout using the Reingold-Tilford algorithm
layout = tree.layout_reingold_tilford(mode='OUT', root=[0])

# Plot the tree using the calculated layout
fig, ax = plt.subplots()
plt.title('Tree Layout using Reingold-Tilford Algorithm')
tree.plot(layout=layout, target=ax)
plt.show()
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