breadth first search

tree = [[1, 2], [3, 4], [5, 6], [7, 8], [9, 10], [11, 12],
        [13, 14], [], [], [], [], [], [], [], []]
data=[0]

while len(data)>0:
    pos=data.pop(0)
    print(pos,end=" ")
    for i in tree[pos]:
        data.append(i)