a) he's probably not a billionaire
b) the NYT made clear that the tax frauds were quite large and over a lot of time. Trump does EVERYTHING by lying and fraud - you should know this by now. It's his standard operating procedure. his first instinct is to lie and cheat. When forced to do something in the correct way he'll do it., but it takes a lot of effort. Look at the criminals he surrounds himself with. You think he's the clean guy in the center of a criminal whirlwind?
"The president has long sold himself as a self-made billionaire, but a Times investigation found that he received at least $413 million in today’s dollars from his father’s real estate empire, much of it through tax dodges in the 1990s.
"Much of this money came to Mr. Trump because he helped his parents dodge taxes. He and his siblings set up a sham corporation to disguise millions of dollars in gifts from their parents, records and interviews show. Records indicate that Mr. Trump helped his father take improper tax deductions worth millions more. He also helped formulate a strategy to undervalue his parents’ real estate holdings by hundreds of millions of dollars on tax returns, sharply reducing the tax bill when those properties were transferred to him and his siblings."