C code to spawn a binary tree of processes using fork(). Tree depth is set by a variable passed as first argument at invocation.

fork.c

#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>

void tree(int n){ //Creates a process tree
    
    if (n==0) return; //We have reached a leaf, so we leave.
    
    int rchild=fork(); //create right child
    if (rchild!=0){ //we are the parent
        int lchild=fork(); //create left child
        if (lchild==0) tree(n-1); //we are the left child, so we create the left subtreee
    }
    else{ //we are the right child
        tree(n-1); //create the right subtree
    }
    
}

int main(int argc, char **argv){
    
    if (argv[1]==NULL) return 1; //we need the depth in order to proceed
    int n=atoi(argv[1]); //conversion of the first parameter to an ineger
    if (n==0) return 0; //if the depth is zero, there is nothing to do
    
    tree(n); //create a tree of depth n
    
    sleep(1000);
    
    return 0;
}