Find all supersets of a collection

supersets.py

collection = [{1, 2, 3, 4, 5},
              {1, 2},
              {1, 2, 3, 4, 5, 6},
              {3, 4, 8},
              {3, 4, 11},
              {3},
              {3},
              {12},
              {1, 2, 3, 4, 5, 6},
              {1, 2, 3, 4, 7, 9},
              {1, 2, 3, 4, 5, 8},
              {3, 5, 10}]

sizes = set()
for i in collection:
    sizes.add(len(i))
sizes = sorted(sizes, reverse=True)

X = dict()
for s in sizes:
    X[s] = []

for s in collection:
    X[len(s)].append(s)


for reference_size in sizes:
    for reference_set in X[reference_size]:
        for s in sizes:
            if s == reference_size:
                X[s][:] = [x for x in X[s] if not x.issubset(reference_set)] +\
                          [reference_set]
            if s < reference_size:
                X[s][:] = [x for x in X[s] if not x.issubset(reference_set)]

updated_collection = []
for s in X:
    updated_collection += X[s]