The tree model is a convenient way of representing the development of a language family and of showing how closely related two of more languages are.
树形模型是表示一个语言家族的发展并显示两种或更多语言的密切相关程度的一种便捷方式。
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But it is obviously very simplified, having a whole language represented by just one branch on a tree doesn't really do justice to all the variations within that language.