Flat tree

output.py

flat = {}
make_tree_flat(tree, flat)

{'a': (None, ['b', 'e']),
 'b': ('a', ['c', 'd']),
 'c': ('b', []),
 'd': ('b', []),
 'e': ('a', ['f']),
 'f': ('e', ['g']),
 'g': ('f', [])}

tree.py

tree = ('a', [
    ('b', [
        ('c', []),
        ('d', []),
    ]),
    ('e', [
        ('f', [
            ('g', []),
        ]),
    ]),
])

def make_tree_flat(tree, dictionary, parent=None):
    node, branches = tree
    children = []
    dictionary[node] = (parent, children)
    for branch in branches:
        name = make_tree_flat(branch, dictionary, parent=node)
        children.append(name)
    return node