要表示文件结构为JSON，可以使用以下代码示例：

import json

# 构建文件结构
file_structure = {
    "root": {
        "folder1": {
            "file1.txt": "This is file 1",
            "file2.txt": "This is file 2"
        },
        "folder2": {
            "file3.txt": "This is file 3",
            "folder3": {
                "file4.txt": "This is file 4"
            }
        }
    }
}

# 将文件结构转换为JSON字符串
json_data = json.dumps(file_structure, indent=4)

# 打印JSON字符串
print(json_data)

运行以上代码，将得到文件结构的JSON表示：

{
    "root": {
        "folder1": {
            "file1.txt": "This is file 1",
            "file2.txt": "This is file 2"
        },
        "folder2": {
            "file3.txt": "This is file 3",
            "folder3": {
                "file4.txt": "This is file 4"
            }
        }
    }
}

可以看到，文件结构被转换为具有嵌套关系的JSON对象。