generateTree from a parsed Tree

generateTree.py

class Tree():
    def __init__(self, val):
        self.val = val
        self.child = []
        
    def addChild(self, t):
        children = self.child
        children.append(t)
        
    def print(self, lev = ""):
        print(lev + self.val)
        for c in self.child:
            c.print(lev + " ")

def solve(s):
    st, last = [], None
    for i in range(len(s)):
        c = s[i]
        
        # generate a new tree & push it into the stack
        if c == "[":
            t = Tree(s[i + 1])
            if not st == []:
                parent = st[-1]
                parent.addChild(t)
            st.append(t)
            
        # pop the tree stack
        elif c == "]":
            last = st.pop()
    return last

solve("[A[B[C][D[E[H]]]]]").print()

# Output
# A
#  B
#   C
#   D
#    E
#     H