Determine merged cell values from mixed merged and unmerged rows in Excel

Question

I have big table with 65K rows of legal cases. Each case has multiple participates so the rows contain participates details, and the first cell of each row is merged and contains the case number :

Table example before the change:

I need a formula that checks all the rows for each case at column B, and if one of them contains "corporate" it will put corporate in column D, else it will put private:

Table example after the change:

How can I do this?