How to create a Node Type uniqueness constraint as a validation expression?

Summary:

How to create a Node Type uniqueness constraint as a validation expression?

Content (please ensure you mask any confidential information):

Want to create a validation similar to a Node Type uniqueness constraint where I only validate for uniqueness for "Bottom Node" = False.

Please help me how I can approach this in writing expression which will check a Parent level Node.Name in one Node Type to compare uniqueness against all Parents Node.Name in a different Node Type within the same application.

Please let me know if need any further details.

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