<｜begin▁of▁sentence｜>### Instruction:
As a recreation therapist, I often need to organize and plan activities for individuals with disabilities or illnesses. Recently, I was tasked with creating a visually appealing and engaging graph representing a tree structure with 5 vertices and a branching factor of 2, to help improve cognitive skills and encourage group interaction.

I need to incorporate undirected edges into the graph and save it as a PNG image using the CairoArrowEdgeDrawer in igraph. Can you guide me on how to achieve this?
### Response:
from igraph.drawing import Plot
from igraph.drawing.edge import CairoArrowEdgeDrawer
import igraph as ig

# Create a graph
g = ig.Graph.Tree(5, 2)  # Tree with 5 vertices and branching factor of 2

# Initialize plot
plot = Plot(bbox=(300, 300), background='white')

# Add vertices to the plot
plot.add(g)

# Use CairoArrowEdgeDrawer to draw the undirected edges
edge_drawer = CairoArrowEdgeDrawer(plot.context)
for edge in g.es:
    from_pt = plot.coords[edge.source]
    to_pt = plot.coords[edge.target]
    edge_drawer.draw_undirected_edge(from_pt, to_pt)

# Save the plot
g.save('tree_graph.png')
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