Реализовать класс TreeBuilder

tree = TreeBuilder()
tree.add(1)
tree.add(2)
 
with tree:
    tree.add(3)
    with tree:
        tree.add(4)
        tree.add(5)
    tree.add(6)
    tree.add(7)
 
print(tree.structure)
# [1, 2, [3, [4, 5], 6, 7]]

levels = 3
count_elements = [3,4,2]
sequence[ count_elements[0] ][ count_elements[1] ].append = 100

class TreeBuilder:
    sequence = []
 
    def add(self, el):
        self.sequence += str(el)+', '
 
    def __enter__(self):
        self.sequence += '['
 
    def __exit__(self, exc_type, exc_value, exc_traceback):
        self.sequence += ']'
 
    @property
    def structure(self):
        return '[' + ''.join(self.sequence) + ']'

import copy
 
 
class TreeBuilder:
    arr = {}
    level = 0
    position = {}
 
    def add(self, el):
        try:
            self.arr[self.level].append(el)
        except:
            self.arr[self.level] = [el]
 
    def __enter__(self):
        self.level += 1
        self.position[self.level] = len(self.arr[self.level-1])
 
    def __exit__(self, exc_type, exc_value, exc_traceback):
        self.level -= 1
 
    @property
    def last(self):
        return max(self.arr.keys())
 
    @property
    def structure(self):
        tmp = copy.deepcopy(self.arr)
        n = self.last
        while n >= 0:
            try:
                tmp[n-1].insert(self.position[n], tmp[n])
                n -= 1
            except KeyError:
                return tmp[0]
 
 
tree = TreeBuilder()
tree.add(1)
tree.add(2)
 
with tree:
    tree.add(3)
    with tree:
        tree.add(4)
        tree.add(5)
        with tree:
            tree.add(0.4)
            tree.add(0.5)
    tree.add(6)
    tree.add(7)
print(tree.structure)
# [1, 2, [3, [4, 5, [0.4, 0.5]], 6, 7]]