how to insert the elements in a list properly?

[length power]

word=["x1","x2","x3","x4","x5"]
w=word[-2:]
del word[-2:]
word.insert(2,w)
word
['x1', 'x2', ['x4', 'x5'], 'x3']

what i want to get is
['x1', 'x2', 'x4', 'x5', 'x3']

how can i insert them ?
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