code: function getLeft(node) {
      let left = node.left;
  
      while (isConcatenation(left)) {
          left = left.right;
      }
      return left;
  }
docs: Get's the right most node on the left side of a BinaryExpression with + operator.
  @param {ASTNode} node - A BinaryExpression node to check.
  @returns {ASTNode} node