In the Silmarillion, I thought it went over creation of the Ents, no mention of Bombadil? Maybe I'm wrong.

Here:

'Conclusion'
There is only one answer to the riddle of Tom Bombadil: that there is no answer. Though we've presented some of the evidence here, this article does no more than dip beneath the surface. It seems, though, that Tom's nature is ultimately undiscoverable, and this is surely a good thing.

Part of the wonder of Tolkien's world is its depth and detail, but it needs its mysteries and unknowns too: if we knew everything about the World of Arda and its inhabitants, there would be no joy of exploration and discovery. If nothing else, Tom Bombadil stands proudly as a symbol of the mysterious, and we should be glad that he does.