Programs are viewed as both functions to be executed and data structures to be analysed, but this has always required encoding, e.g.\ of a lambda-term to a syntax tree, so that a self-interpreter could not be applied to itself directly, but only to its code. Further, the code of a typed program should have a distinctive type. In a tree calculus, however, program analysis can be supported directly, without encodings, including the self-application of a breadth-first self-interpreter of type

[

{\bf bf} :\forall X. \forall Y. (X\to Y) \to (X\to Y); .

]