Hi Sarma,

1-you need to a csv file account record less than or equal to 5 to check insert record in Account Object.
2-you need to a csv file account record more than 5 to check error.
3-you can not insert duplicate record name it will throw error.
Your problem has been solved.

VisualforcePage:
<apex:page controller="importDataFromCSVController">
    <apex:form >
        <apex:pagemessages />
        <apex:pageBlock >
            <apex:pageBlockSection > 
                  <apex:inputFile value="{!csvFileBody}"  filename="{!csvAsString}"/>
                  <apex:commandButton value="Upload" action="{!importCSVFile}"/>
            </apex:pageBlockSection>
        </apex:pageBlock>
        <apex:pageBlock >
           <apex:pageblocktable value="{!accList}" var="acc">
              <apex:column value="{!acc.name}" />
              <apex:column value="{!acc.AccountNumber}" />
              <apex:column value="{!acc.Type}" />
              <apex:column value="{!acc.Accountsource}" />
              <apex:column value="{!acc.Industry }" />
        </apex:pageblocktable>
     </apex:pageBlock>
   </apex:form>
</apex:page>

Apex class:
public class importDataFromCSVController {
    public Blob csvFileBody{get;set;}
    public string csvAsString{get;set;}
    public String[] csvFileLines{get;set;}
    public List<account> acclist{get;set;}
    public List<String> accctNames{get;set;}
    public List<account> newAccts{get;set;}
    public boolean flag=true;
    public importDataFromCSVController(){
        csvFileLines = new String[]{};
            acclist = New List<Account>();
        newAccts = New List<Account>();
        accctNames = new List<String>();
    }  
    public void importCSVFile(){
        csvAsString = csvFileBody.toString();
        csvFileLines = csvAsString.split('\n'); 
        if(csvFileLines.size()>=1 && csvFileLines.size()<=5){
            if(flag==true){
                for(Integer i=1;i<csvFileLines.size();i++){
                    Account accObj = new Account() ;
                    string[] csvRecordData = csvFileLines[i].split(',');
                    
                    accObj.name = csvRecordData[0] ;             
                    accObj.accountnumber = csvRecordData[1];
                    accObj.Type = csvRecordData[2];
                    accObj.AccountSource = csvRecordData[3];   
                    accObj.Industry = csvRecordData[4];  
                    accctNames.add(accObj.Name);
                    acclist.add(accObj);   
                }
                List<Account> existingAccts =new List<Account>();
                existingAccts = [SELECT Id, Name FROM Account where Name IN:accctNames];
                
                Map<String, Id> acctNamesIdMap = new Map<String, Id>();
                // load the map - this will help you find out if an account name exists already
                for (Account acct : existingAccts)
                {
                    acctNamesIdMap.put(acct.Name, acct.Id);
                    System.debug('******Sai******');
                    ApexPages.Message errormsg = new ApexPages.Message(ApexPages.severity.ERROR,'Account ' + acct.Name + ' already exists, change Account Name and try again');
                    ApexPages.addMessage(errormsg);
                }
                
                for (Account acct : acclist)
                {
                    //if account name does not exist in map, add it to list of new accounts
                    if (!acctNamesIdMap.containsKey(acct.Name))
                    {
                        newAccts.add(acct);
                        
                    }
                }
                try
                {
                    insert newAccts;
                }
                catch (Exception e)
                {
                    ApexPages.Message errormsg = new ApexPages.Message(ApexPages.severity.ERROR,'Account Name already exist, change Account Name and try again');
                    ApexPages.addMessage(errormsg);
                }
                flag=false;
            }
            else{
                ApexPages.addmessage(new ApexPages.message(ApexPages.severity.ERROR,'Account Name already exist, change Account Name and try again')); 
            }
        }
        else{
            ApexPages.addmessage(new ApexPages.message(ApexPages.severity.ERROR,'Please upload Account records less than 5')); 
        }
    }
}

Please let me know if you have any query.
Please mark it as best Answer if you find it helpful.

Thank You
Ajay Dubedi