In chapter 1.2.2 you can read about SICP view of tree recursion as a common
pattern of computation.As an example it proposes the computation of Fibonacci numbers.
Below you can check my F# version of the book's method for calculating them.

module FibonacciImplemtation
open System

let  rec  fib n =
  if n = 0  then 0 else
   if n = 1 then 1 else
    fib (n - 1) + fib (n - 2)

// test
let testFib = fib 7