title: Merge two sub graphs in neo4j
body: <p>I have two subgraphs in the following way</p>
  
  <pre><code>                      (root1)                    (root2)
                         / | \                      / | \
                        /  |  \                    /  |  \
                       /   |   \                  /   |   \
                     (a1) (a2) (a3)             (b1) (b2) (b3)
  </code></pre>
  
  <p>I want to create a new graph by merging above two</p>
  
  <pre><code>                               (root)
                            /  /  /  \  \  \
                         (a1)(a2)(a3)(b1)(b2)(b3)
  </code></pre>
  
  <p>Is there a way to just replace one of the root nodes in one of the tree instead of iterating all the children of one tree, disconnect the current root, and connect to new root?</p>