create a mapping values for node roles

my values file has a nodeRole as key value pair however my deployment file throws an error as it can only only accept string and not mapping values. How do I fix this?

values.yaml :

 nodeRoles:
          key: 
          value: 

deployment.yaml:

nodeSelector:   
    nodeRoles:
          key: {{.Values.nodeRoles.key}}
          value: {{.Values.nodeRoles.value}}

How do I make this work? I only want the deployment to accept key value pair and not string