Well silicon trees are the center piece of a hypothesis postulated by Людин Рɣси(don't ask me to pronounce that or write it in English). He's a Russian YouTubers and flat earth theorist. According to his hypothesis a significant number of geological formations are actually remains of silicon based trees from ancient times.
He postulates that mountains are actually ancient silicon based tree stomps and that the similarity between tree stomps and mountains is not a coincidence. He also goes on to say that scientists know the truth about our earth and they're trying to keep the rest of the world in the dark.
His theory also goes so far as to suggest that giants once walked the earth. His theories aren't so far fetched if you ask me because we only know what we know about the earth's history from what we read in books and see on TV. It's quite possible that what he's saying is right, but the science behind what he's saying isn't exactly feasible if you ask me.
Silicon on its own isn't as easy to bond with as carbon and as such silicon based life forms are pretty hard to perceive. As far as wether or not silicon trees exist, there isn't any official record of such. But if you meet into Людин Рɣси's argument then just about every mountain is a silicon tree.
So was the Earth originally covered with truly giant silicon trees, many miles high, in the distant past that were systematically cut down?
To my understanding, silicon trees are plantation that were very high and perhaps strong. You could say that they were giant trees. It was said that these trees had a connection to the center of the Earth and it actually protected the Earth.
But the question there is that are they real or there is a conspiracy to hide the truth.