Can anyone tell why do I get an infinite loop? While-loop

I wanna replace 1 to * and 0 to ” to make a tree.
I did this with for-loop.

picture = [
  [0,0,0,1,0,0,0],
  [0,0,1,1,1,0,0],
  [0,1,1,1,1,1,0],
  [1,1,1,1,1,1,1],
  [0,0,0,1,0,0,0],
  [0,0,0,1,0,0,0]
]
i = 0
while i < len(picture):
    j = 0
    while j < len(picture[i]):
        if picture[i][j] == 0:
            print('', end='')
        else:
            print('*', end='')
    i += 1

>Solution :

try this.

picture = [
  [0,0,0,1,0,0,0],
  [0,0,1,1,1,0,0],
  [0,1,1,1,1,1,0],
  [1,1,1,1,1,1,1],
  [0,0,0,1,0,0,0],
  [0,0,0,1,0,0,0]
]
i = 0
while i < len(picture):
    j = 0
    while j < len(picture[i]):
        if picture[i][j] == 0:
            print('', end='')
        else:
            print('*', end='')
        j += 1
    print()
    i += 1

If you want this output

*
***
*****
*******
*
*