617. Merge Two Binary Trees

class Solution {
    public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {
      if (t1 == null && t2 == null) return null;

      if(t1 == null) return t2;
      if(t2 == null) return t1;
      
      TreeNode newRoot = new TreeNode(t1.val + t2.val);
      newRoot.left = mergeTrees(t1.left, t2.left);
      newRoot.right = mergeTrees(t1.right, t2.right);
      return newRoot;       
    }
}