open class FileItem(val file: File) : ListItem {
    override val isDirectory: Boolean
        get() = file.isDirectory

    override val name: String
        get() = file.name
}

class FSDataProvider : DataProvider<FileItem> {
    private val rootFolder = Environment.getExternalStorageDirectory()

    override suspend fun getRoot(): List<FileItem> =
            rootFolder.listFiles().map { FileItem(it) }

    override suspend fun getByParent(listItem: FileItem): List<FileItem> =
            listItem.file.listFiles().map { FileItem(it) }
}

TreeListDialogBuilder(this, FSDataProvider()).apply {
    title = "Select a folder"
    positiveButtonTitle = "Select"
    positiveButtonClick = {doSomethind(it)}
}.build().show()