In Jesus' parable, what did a man find hidden in a field, then sell all he had to buy the field?

Answer: Treasure

The kingdom is like treasure hidden in a field; in his joy the finder sold all he had and bought that field.

“The kingdom of heaven is like treasure hidden in a field. When a man found it, he hid it again, and in his joy he went and sold all he had and bought that field.”— Matthew 13:44 (BSB)