input: Write a python function to convert binary tree to HTML table where each node is represented with its value, left child and right child. 
  assert convert_tree_to_html(Node(1, Node(2), Node(3))) == "<table><tr><th>Value</th><th>Left</th><th>Right</th></tr><tr><td>1</td><td>2</td><td>3</td></tr></table>"
  assert convert_tree_to_html(Node(10, Node(5), Node(20, Node(15), Node(25)))) == "<table><tr><th>Value</th><th>Left</th><th>Right</th></tr><tr><td>10</td><td>5</td><td>20</td></tr><tr><td>20</td><td>15</td><td>25</td></tr></table>"
  assert convert_tree_to_html(Node(1)) == "<table><tr><th>Value</th><th>Left</th><th>Right</th></tr><tr><td>1</td><td></td><td></td></tr></table>"
output: class Node:
      def __init__(self, value, left=None, right=None):
          self.value = value
          self.left = left
          self.right = right
  
  def convert_tree_to_html(node):
      def node_to_html(n):
          if n is None:
              return ""
          left_val = n.left.value if n.left else ""
          right_val = n.right.value if n.right else ""
          return f"<tr><td>{n.value}</td><td>{left_val}</td><td>{right_val}</td></tr>" + node_to_html(n.left) + node_to_html(n.right)
  
      html = "<table><tr><th>Value</th><th>Left</th><th>Right</th></tr>"
      if node:
          html += node_to_html(node)
      html += "</table>"
      return html