How to Import data to sql from Excel data table by c#

Problem

How to write code import data table to SQL server 2012 .

Details

I have excel sheet name InvoiceData.xlsx have two columns

UnitCode    CurrentMeterReading  
21544                2900  
22152                9000  
19822                9200  

I get success data from excel sheet to datatable as following :

public System.Data. DataTable Showdataprint()  
        {  
  
            OleDbConnection con = new OleDbConnection(connectionString);  
            con.Open();     
            string str = @"SELECT  [UnitCode],[CurrentMeterReading] FROM  [Sheet1$]";  
            OleDbCommand com = new OleDbCommand();  
            com = new OleDbCommand(str, con);  
            OleDbDataAdapter oledbda = new OleDbDataAdapter();  
            oledbda = new OleDbDataAdapter(com);  
            DataSet ds = new DataSet();  
            ds = new DataSet();  
            oledbda.Fill(ds,"[Sheet1$]");  
            con.Close();  
            System.Data.DataTable dt = new System.Data.DataTable();  
            dt = ds.Tables["[Sheet1$]"];  
            return dt;  
  
        }  

I get successfully data from excel to Datatable Now I need to Import data from datatable to sql server 2012 TableName : WahInvoice PK : Serial

CREATE TABLE [dbo].[WAHInvoice](  
    [Serial] [int] NOT NULL,  
    [Year] [int] NULL,  
    [Month] [int] NULL,  
    [UnitCode] [int] NULL,  
    [CurrentReadingDate] [date] NULL,  
    [CurrentMeterReading] [decimal](18, 2) NULL,  
 CONSTRAINT [PK_WAHInvoice_1] PRIMARY KEY CLUSTERED   
(  
    [Serial] ASC  
  
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]  
) ON [PRIMARY]  

I need to know how to Import data from excel to sql .

suppose i have data on sql in table WahInvoice

with max serial 2000 this meaning data will be as following :

Serial  UnitCode          CurrentMeterReading  
 2001   21544                2900  
 2002   22152                9000  
 2003   19822                9200  

and all values for columns remaining will be null .

Actually what i write for Import data to sql under import button Under Import button click i write as following :

System.Data.DataTable dt = new System.Data.DataTable();  
                    dt = Showdataprint();  
//How to import datatable to sql server 2012