Well..it's not a binary search tree.So we need to traverse
entire binary tree and check with the all node elements and
find the max value.
struct node
{
int data;
struct node *l;
struct node *r;
};
typedef struct node *nd;
int maximum(nd root)
{
static int max;
nd cur = root;
if(cur!=NULL)
{
if(cur->data>max)
max=cur->data;
maximum(root->l);
maximum(root->r);
}
return max;
}

Well..it's not a binary search tree.So we need to traverse
entire binary tree and check with the all node elements and
find the max value.
struct node
{
int data;
struct node *l;
struct node *r;
};
typedef struct node *nd;
int maximum(nd root)
{
static int max;
nd cur = root;
if(cur!=NULL)
{
if(cur->data>max)
max=cur->data;
maximum(root->l);
maximum(root->r);
}
return max;
}

3333598209374158490386452138699.3

The Largest Node in the Binary tree is the Rightmost node 
of the tree.
Hence we would traverse the Tree Till The Rightmost child 
of the node is traversed.

the code is as follows:


#include<stdio.h>
#include<conio.h>

struct node
{
  int data;
  struct node *left,*right;
}*tree;

struct node* MAX(struct node* q)
{ 
    struct node* temp;  
 while(q->right!=NULL)
    {
       temp=q;
        q=q->right;
     }
 return temp;
}


this algorithm will find the largest element of the tree in 
o(log n).