If I were given a free holiday, I would like to visit Los Angels, because I have been thinking about Yosemite National Park for a long time. There is the biggest trees in the world and I saw a picture of them in a text book before. If the tree falls down, they will hollow out the tree and make a big tunnel which is big enough to drive a car through. Due to the large size of the trees, it’s impossible to move them.
Don’t you think it is amazing?

Does this sound natural?

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It seems you're learning both UK and US English. A "holiday" in the US is referred to as a vacation if you wanted to use this as an alternative word.

Los Angels is spelled Los Angeles.

Change "There is the biggest trees in the world and I saw a picture of them in a text book before." to "It contains the biggest trees in the world, and I saw a picture of them in a text book before."

"If a tree falls down, they will hollow out the tree and make a big tunnel which is big enough to drive a car through." Change "the" to "a" since you're not talking about any specific tree.