https://domain name/services/data/v36.0/composite/tree/account/

{
"records" :[{
    "attributes" : {"type" : "Account", "referenceId" : "ref1"},
    "name" : "SampleAccount1",
    "phone" : "1111111111",
    "website" : "www.salesforce1.com",
    "industry" : "Banking"
    },{
    "attributes" : {"type" : "Account", "referenceId" : "ref2"},
    "name" : "SampleAccount2",
    "phone" : "2222222222",
    "website" : "www.salesforce2.com",
    "industry" : "Banking"
    },{
    "attributes" : {"type" : "Account", "referenceId" : "ref3"},
    "name" : "SampleAccount3",
    "phone" : "3333333333",
    "website" : "www.salesforce3.com",
    "industry" : "Banking"
    },{
    "attributes" : {"type" : "Account", "referenceId" : "ref4"},
    "name" : "SampleAccount4",
    "phone" : "4444444444",
    "website" : "www.salesforce4.com",
    "industry" : "Banking"
    }]
}

curl -X POST -H "Authorization: OAuth 00D280000013mzk!AQUAQKnGCLaJo2F0fmpegSMy4VSBCXVPJygVZG8Zf2rj7E6NJE3yueMITIxIAJT0YVjxpoJRe4PRR6okbPH6A86DAVMGVAEH" -H "Content-Type: application/json" -H "Cache-Control: no-cache" -H "Postman-Token: 7db97417-e223-1319-a64e-4a72236b89dd" -d '{
"records" :[{
    "attributes" : {"type" : "Account", "referenceId" : "ref1"},
    "name" : "SampleAccount1",
    "phone" : "1111111111",
    "website" : "www.salesforce1.com",
    "industry" : "Banking"
    },{
   "attributes" : {"type" : "Account", "referenceId" : "ref2"},
    "name" : "SampleAccount2",
    "phone" : "1111111111",
    "website" : "www.salesforce1.com",
    "industry" : "Banking"
    }]
}' "https://domain name/services/data/v36.0/composite/tree/account/"