public boolean isSubtree(TreeNode root1, TreeNode root2) {
		if (root1 == null && root2 == null) {
			return true;
		}
		if (root1 != null && root2 == null) {
			return true;
		}
		if (root1 == null && root2 != null) {
			return false;
		}
		boolean isSubtree = isSubtreeHelper(root1, root2);
		return isSubtree;
	}