Task: Insert a document in MongoDB

n8n workflow JSON:
{"nodes":[{"name":"On clicking 'execute'","type":"n8n-nodes-base.manualTrigger","position":[220,320],"parameters":{},"typeVersion":1},{"name":"Set","type":"n8n-nodes-base.set","position":[420,320],"parameters":{"values":{"string":[{"name":"my_key","value":"my_value"}]},"options":{}},"typeVersion":1},{"name":"MongoDB","type":"n8n-nodes-base.mongoDb","position":[620,320],"parameters":{"fields":"my_key","operation":"insert","collection":"n8n-collection"},"credentials":{"mongoDb":"mongodb_credentials"},"typeVersion":1}],"connections":{"Set":{"main":[[{"node":"MongoDB","type":"main","index":0}]]},"On clicking 'execute'":{"main":[[{"node":"Set","type":"main","index":0}]]}}}