gistfile1.txt

i1 = ["B,E,F", "A,B,C,D", "D,G,I", "G,H"]

class Node:
    def __init__(self, name):
        self.name = name
        self.children = set()

    def __repr__(self):  # just for debugging
        return f"{self.name}: {self.children}"
    
    def print(self, depth=0):
        print("." * depth + self.name)
        for c in sorted(self.children, key=lambda x: x.name):
            c.print(depth=depth+1)
            
def create(l):
    apices = {}
    all_nodes = {}
    for s in l:
        x = s.split(',')
        head = x[0]
        tail = x[1:]
        if head in all_nodes:
            cur_node = all_nodes[head]
        else:
            cur_node = Node(head)
        
        for element in tail:
            if element in apices:
                apices.pop(element)
            if element in all_nodes:
                cur_child = all_nodes[element]
            else:
                cur_child = Node(element)
            cur_node.children.add(cur_child)
            all_nodes[element] = cur_child
            
        if head not in all_nodes:
            apices[head] = cur_node
        all_nodes[head] = cur_node

    return list(apices.values())
    
for apex in create(i1):
    apex.print()
    
"""
A
.B
..E
..F
.C
.D
..G
...H
..I
"""