In historical linguistics, tree model (tree theory) is a model of language evolution, similar to the concept of genealogy. Tree theory believes that languages ​​are constantly differentiated. They assume that a primitive common language once existed.This primitive common language was divided into several different languages and further divided into what are various languages ​​in the world today. Tree model is perhaps the most well-known representation of language evolution. As early as the 16th century, missionaries and European travelers were noting the similarities between their mother tongue and various other languages. The idea of a common ancestral language, which we now call Proto-Indo-European, was first mentioned in 1786 by Sir William Jones. The pedigree tree theory continued to evolve in the 19th century, as more language families were included and developed.

With the Tree model, it is easy to quickly group languages together and spot similarities. However, there are a few caveats to using this method. It cannot fully represent language diversification, highlight language sharing, and point to specific similarity types between languages not of the same family. Another point of contention is that it is difficult to substantiate new micro-groupings and subfamilies of languages. Frequent loanwords and language borrowing can make it difficult to determine earlier versions of a language. Obviously, the pedigree tree theory simplifies the complex language phenomenon.