<｜begin▁of▁sentence｜>### Instruction:
Given a graph with nodes [1, 2, 3, 4, 5] and edges [(1, 2), (1, 3), (2, 4), (2, 5)], is this graph a tree? Additionally, what happens to the property of being a tree if an edge is added between nodes 3 and 4?
### Response:
import networkx as nx

# Create a new graph
G = nx.Graph()

# Add edges to the graph
G.add_edges_from([(1, 2), (1, 3), (2, 4), (2, 5)])

# Use the is_tree API to check if the graph is a tree
is_a_tree = nx.is_tree(G)

print(f'Is the graph a tree? {is_a_tree}')

# Add an edge that creates a cycle
G.add_edge(3, 4)

# Check if the graph is a tree after adding the edge
is_a_tree_now = nx.is_tree(G)

print(f'After adding an edge between 3 and 4, is the graph still a tree? {is_a_tree_now}')
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