Prettyprint to a file?

What you need is Pretty Print pprint module:

from pprint import pprint

# Build the tree somehow

with open('output.txt', 'wt') as out:
    pprint(myTree, stream=out)

Another general-purpose alternative is Pretty Print's pformat() method, which creates a pretty string. You can then send that out to a file. For example:

import pprint
data = dict(a=1, b=2)
output_s = pprint.pformat(data)
#          ^^^^^^^^^^^^^^^
with open('output.txt', 'w') as file:
    file.write(output_s)