Negotiating salary in investment bank/ global markets

Wise brethren, I humbly seek your advice

Profile: 10 years work experience post MBA, exp in Front office deal teams, risk , all of it in structured finance.

I am currently in the process of negotiating an offer for Structured Credit Financing role ( front office/deal team) in a European bank . The position is not in NY,LDN,FFT.

I hold a prior live offer from a large buy side credit fund in their FP&A / Finance role which I had received 1 month back (approx 20% hike)

1. Is it safe to use the earlier live offer while negotiating with the bank now?

2. Is there a possibility of it backfiring from HR / hiring manager, if it is disclosed?

- why are you shopping for offers if you currently hold one?

- why didn't you disclose earlier in the interview process that you already held an offer?

3. Is it standard practice in the IB/GM business to negotiate offers based on what the candidate currently holds? Does the HR expect it or is this unprofessional/frowned upon?

4. If I hold a live offer, does that become the base for any future negotiations or is the prior salary itself taken as base for negotiations?

5. How should we provide an estimate for expected salary from the current base and live offer?

Please kindly help.