Not so, thanks to the distinction between narrow and wide content. So it depends what you mean by "trees." If you're talking about trees as such, or as we commonly conceive of them, their independent reality, which is to say the sufficiency of that conception must be tentative, since we may eventually alter our conceptions as we come to understand everything's place in the totality of nature. What will people think of trees a million years from now? Will they picture them like we do? If not, how do we know our conception is best, as in adequate to the external, independent facts?

If, however, you're talking about the referent of "trees," the external X that we understand with our human conception or stereotype of trees, we can affirm the actuality of some such X. But notice how empty that affirmation is without any narrow, conceptual content. We'd be talking about the quantum mechanical upshot that makes for what we perceive as trees, which upshot no one really understands. So what does it mean to say trees as objective placeholders, as what Kant called noumena or things in itself are actually real?

Think of it this way. We're like Neo in the matrix. We might suspect there's an inhuman reality out there which amounts to the whole of the universe with no parts carved up in merely human, parochial ways. But understanding that totality would be a transhuman, godlike act. That's why in the movie, Neo couldn't picture the reality outside the matrix until he was shown it, or until he stepped outside his limited conceptions. Getting past our human conception of trees to see what trees really are, independent of all human interests and interactions is a conundrum of modern philosophy.

You can say that philosophy is empty, if you like, but if you couldn't demonstrate why that's so, there would be no obvious need for a philosopher to respond to the prejudice you'd be evincing.