Binary Tree Design Algorithm

[Googol]

I am currently learning how to use binary trees, but I am having trouble getting started on how to design basic methods. The simplest of the methods I need to write is finding the maximum number in an unsorted binary tree. I think if I could just see a method I could get an idea on how to travel throughout a binary tree.
I know that sending a value such as 0 for my initial max is a bad idea just in case all of the input is negative, but I am not sure how to grab some leaf from the tree as my starting max value.


The input is something like this. (((10 16) -2 25) (33 4) 21 59)

public static int findMax (Object tree) 
{
  return findMax2(tree, 0);
}

public static int findMax2 (Object tree, int max)
{
	if (method returning boolean for tree)
	{
		int left = findMax2(lhs((Cons)tree), max);
		int right = findMax2(rhs((Cons)tree), max);
		max = left > right ? left : right;
	}
	else if (method returning boolean for leaf)
	{
		int curr = (int) (Integer) tree;
		max = curr > max ? curr : max;
	}

	return max;
}

[KevinWorkman]

You could set your initial value to negative infinity, or just the first value you come across.