Trump borrowed $11.2 million from the institution for a mortgage on a house that now sits empty and unrented. Only a few months later, that same bank's CEO was named to a Federal Reserve position (details here). While Trump likely had nothing to do with that appointment, it nonetheless creates a massive conflict of interest on both the President's part and that of the bank. Trump's loan was likely approved simply because he's President, given it generates no revenue and sits empty, making it a risky loan prospect.
In contrast, in order to avoid any potential ethical problem, President Obama never refinanced his personal home mortgage during his entire presidency, even though that could have saved him a small fortune.
Trump's behavior is likely not illegal on this issue. But it nonetheless demonstrates a President with a complete lack of ethical standards and self policing. The bank is in much the same boat, granting loans as political favors on rental property that generates no revenue.