Compare two binary trees

Just compare two binary trees -- return true or false

//Simple binary tree
class btelement
{
public int value;
public btelement left = null;
public btelement right = null;
public btelement(int v)
{
value = v;
}
}

// simple filling
btelement root1 = new btelement(1);
root1.left = new btelement(2);
root1.left.left = new btelement(4);
root1.right = new btelement(3);
root1.right.left = new btelement(5);

btelement root2 = new btelement(1);
root2.left = new btelement(2);
root2.left.left = new btelement(3);
root2.right = new btelement(3);
root2.right.left = new btelement(5);

//Simple comparison
label1.Text = comparetrees(root1 , root2 ).ToString() ;

// Recursive binary tree comparisons
private bool comparetrees(btelement a, btelement b)
{
if (a == null)
{//make sure both are null else return false
if (b == null) return true;
else return false;
}
else
{
if (b == null) return false;
else
{
// Do the real work
if (a.value == b.value)
{// if values aer same check children
if ((comparetrees(a.left, b.left)) &&
(comparetrees(a.right, b.right)))
return true;
else return false;
}
else return false;
}
}
}

Very good code, however I am concerned with memory usage for large trees while making recursive calls.
Can we do it non recursively or in more optimal way?