<｜begin▁of▁sentence｜>### Instruction:
Given a tree graph with 5 vertices (each with degree 2) and a custom Cairo-based vertex drawer, how can the AbstractCairoVertexDrawer subclass be implemented to draw the vertices of the graph using a Kamada-Kawai layout?
### Response:
from igraph import Graph, plot
from igraph.drawing import BoundingBox
from igraph.drawing.baseclasses import AbstractCairoVertexDrawer
import cairo

# Define your custom vertex drawer by subclassing the AbstractCairoVertexDrawer class
class MyVertexDrawer(AbstractCairoVertexDrawer):
    def __init__(self, context, bbox, palette=None, layout=None):
        super().__init__(context, bbox, palette, layout)

    def draw(self, vertex):
        # Custom drawing code goes here
        self.context.arc(self.layout[vertex][0], self.layout[vertex][1], 5, 0, 2 * math.pi)
        self.context.fill()

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

# Establish your layout
layout = g.layout('kk')

# Set up Cairo context and bounding box
surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, 300, 300)
ctx = cairo.Context(surface)
bbox = BoundingBox(300, 300)

# Initialise your custom vertex drawer
vertex_drawer = MyVertexDrawer(ctx, bbox, layout=layout)

# Draw the vertices
g.vs['drawer'] = vertex_drawer
for vertex in g.vs:
    vertex_drawer.draw(vertex.index)

# Saving the graph to a file
surface.write_to_png('custom_vertex_draw.png')

plot(g, 'graph_with_custom_vertices.png')
<|EOT|>
