gistfile1.txt

class Node:
    def __init__(self, name: str, parent: 'Node' = None):
        self.name = name
        self.parent = parent
        self.children = []

    def add_child(self, obj: 'Node'):
        self.children.append(obj)

    @property
    def parent_name(self) -> str:
        return self.parent.name if self.parent else None

    def __repr__(self) -> str:
        return f'Node(name={self.name!r}, parent={self.parent_name!r}, children_len={len(self.children)})'

    def to_dict(self) -> dict:
        def _to_dict(node: Node):
            return {child.name: _to_dict(child) for child in node.children}

        return _to_dict(self)

source = [
    (None, 'a'),
    (None, 'b'),
    (None, 'c'),
    ('a', 'a1'),
    ('a', 'a2'),
    ('a2', 'a21'),
    ('a2', 'a22'),
    ('b', 'b1'),
    ('b1', 'b11'),
    ('b11', 'b111'),
    ('b', 'b2'),
    ('c', 'c1'),
]

expected = {
    'a': {'a1': {}, 'a2': {'a21': {}, 'a22': {}}},
    'b': {'b1': {'b11': {'b111': {}}}, 'b2': {}},
    'c': {'c1': {}},
}


def to_tree(source):
    name_by_node = dict()
    name_by_node[None] = Node('ROOT', None)

    for parent, child in source:
        parent_node = name_by_node[parent]
        if child not in name_by_node:
            name_by_node[child] = Node(child, parent_node)
        parent_node.add_child(name_by_node[child])

    return name_by_node[None].to_dict()
    
assert to_tree(source) == expected