Why did Charley think that Grand Central Station was growing like a tree, pushing out new corridors and staircases like roots?

The Grand Central Station of the New York is huge. It has two levels. Charley had been into the Grand Central hundreds of times. Every time he had a new experience. He would bump into new corridors and new staircases. He had lost his way there many times. Once, he got into a tunnel a mile long and came up in the lobby of a hotel. Another time, he came up in an office building. Therefore, he had begun to suspect that the Grand Central was ever pushing up new corridors and new staircases like roots of a tree. Perhaps, new corridors and tunnels were trying to reach Times Square and Central Park, but his most amazing experience was when he lost his way and reached the third level. He was in a hurry to reach home one evening. He wanted to take a train on the second level. However, the corridor led him to the third level which was not supposed to exist. The strangest thing was that the corridor had led him into the past. Everything, including people, on third level, was about a century old. It was that of 1894.