Note: you can export the figure to a file, to make an arbitrarily large image:
plt.savefig("mytree.png", dpi=300)
You may want to play with the dpi (dots per inch) parameter, and also with the figure size -- (20,20) figure size until you get something you like.
Or if PNG doesn't work well, try exporting as PDF:
plt.savefig("mytree.pdf")
You might also play with adding the fontsize=8
(or some other size), keyword parameter into the plot_tree
function.