The naive recursive definition of Fibonacci is: $F(n) = \begin{cases} 0 & \text{if } n=0 \\ 1 & \text{if } n=1 \\ F(n-1) + F(n-2) & \text{if } n \geq 2 \end{cases}$ How many total function calls (nodes in the call tree, including the initial call) are made when computing $F(6)$ using this naive recursion?