<｜begin▁of▁sentence｜>### Instruction:
Given a small tree graph generated with igraph (with 5 vertices, branching factor of 2), how can you use a subclass of AbstractCairoGraphDrawer to draw this graph on a Cairo canvas and save the result as an image ('sample_graph.png')? Note: The subclass should implement the draw method which utilizes a Cairo context and a bounding box for drawing.
### Response:
import igraph as ig
from igraph.drawing import Plot
from igraph.drawing.cairo import CairoGraphDrawer

# Create a small sample graph
g = ig.Graph.Tree(5, 2)

# Create a plot with 300x300 pixels
plot = Plot(bbox=(300, 300))

# Access the Cairo context from the plot
cr = plot.ca

# Create an instance of a graph drawer that can draw on the Cairo context
drawer = CairoGraphDrawer(cr, plot.bbox)

g.show = lambda: drawer.draw(g)  # Assuming the CairoGraphDrawer subclass implements draw
# To visually see the graph, depending on your environment, you might directly save it to a file or display it
plot.save('sample_graph.png')
<|EOT|>
