To start you need a master private key. For me, the easiest way to do this is with bcoin and its default wallet in regtest mode:
$ bwallet-cli mkwallet --mnemonic='zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo wrong' --id=zoo
$ bwallet-cli --id=zoo master
{
"encrypted": false,
"key": {
"xprivkey": "tprv8ZgxMBicQKsPdCttbKDzsuDzypKyWMDfGbzR5YsQe3dnPg6B69PPEaxawUuaanULMtgA8Etd9DaqDVSEBSbScA9xTsdR8PRfPsJZwKS3dJQ"
},