[Python] Create nested lists based on split of characters

I have a list made by strings, correctly cleaned (split(',') can be safely used), and correctly sorted depending on numbers. As a small example:

l = ['C1', 'C1,C2', 'C2,C3', 'C3,C4', 'C4', 'C5', 'C5,C6', 'C6,C7', 'C7,C8', 'C8', 'C10', 'C10,C11', 'C11,C12', 'C12,C13', 'C13']


What I'm trying to achieve is to create as many sublists that start and end with single strings, that is:

[
['C1', 'C1,C2', 'C2,C3', 'C3,C4', 'C4'],
['C5', 'C5,C6', 'C6,C7', 'C7,C8', 'C8'],
['C10', 'C10,C11', 'C11,C12', 'C12,C13', 'C13']
]


I thought to add some logic like the following code, but I'm not sure if I'm on the correct way:

tl = []

for i in l:

# just get the variable
val = i

tl.append(val)

# split by ,
val_split = len(i.split(','))

# check if the value is the first element of the list (C1)
if val == l[0]:
print(1, val)
# check if the split of the character is longer than 2 (C1,C2)
elif val_split > 1:
print(2, val)
# check is the split of the character siis equalt to 1 (C4)
elif val_split == 1:
# here the code should compare if the character is equal to the last value of the nested list. If yes go with teh next value (C5)
if val != tl[-1]:
print(3, val)
else:
print(4, val)

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