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Is the word in bracket requires in the following sentence?

We were standing at the bus stop (while) waiting for the bus when the plane plunged into the crowd.

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Goldenboy1

Is the word in bracket required in the following sentence?

We were standing at the bus stop (while) waiting for the bus when the plane plunged into the crowd.

No – it's optional.

However, (while) waiting for the bus is redundant: you'd have no other reason for standing at the bus stop.