Long queues formed outside Cross’s funeral home in Lower Gerald Griffin Street as mourners sympathised with his family.
The mourners were led by Mr Treacy’s partner, Amanda, and their two children, Danielle, 14, and Kieran, 10.
A man, aged 29, was still in custody last night as part of the murder investigation.
His period of detention was extended on Wednesday night by Limerick District Court on the application of Chief Superintendent David Sheehan.
A brother of the man in custody has already been released.
Both were friends of Darren Coughlan, 18, who died after a vicious assault five years ago.
Richard Treacy, a brother of Daniel Treacy, was one of the three youths jailed for the manslaughter of Darren Coughlan.
Gardaí are satisfied the murder was a revenge attack for the death of Darren Coughlan. The car used by the gunman was found burnt out near Beale strand outside Ballybunion and it has been brought back to Limerick where it has been forensically examined.
Up to 100 gardaí have been deployed to the murder investigation. Daniel Treacy was shot dead at the Topaz filling station on Ennis Road at around 6.30am on Monday while having a cup of tea having delivered bread to the filling station shop. He was hit three times in the head by bullets fired from a semi-automatic handgun.
His father Phil, has had full-time armed Garda protection on his bread-round since evidence of another son, Owen, helped jail five members of the McCarthy-Dundon gang for life in 2003 when they were convicted of the murder of crime boss, Kieran Keane.
Keane and Owen Treacy were abducted and brought to Drombanna on the outskirts of the city in January 2003.
Keane was shot dead and after the gun jammed, Owen Treacy was stabbed 17 times and left for dead.