There were at least 30 people there to see the artwork at any one time, according to BBC Radio London reporter Anna O'Neill, since it first appeared on Hornsey Road, in Finsbury Park, on Sunday morning.
It shows a "great arterial spray of green paint" across a white wall, accompanied by a "classic Banksy-style stencil", according to James Peak, who created the BBC Radio 4 series The Banksy Story.
The colour of the green paint used matches that used by Islington Council for signs in the local area, which Mr Peak said demonstrated Banksy's famous eye for detail.
Before the artist confirmed it was his piece of work, Islington councillor Flora Williamson said it would be "incredible" to have a Banksy artwork "right in the middle of social housing and one of the poorest parts of the borough".
The elusive artist usually confirms his work on his website and social media, and on Monday he posted images of the artwork on Instagram with no caption.
Speaking to BBC Radio 4's Today programme, Mr Peak said that by incorporating a tree into the artwork, Banksy has "solved an emerging problem" of people trying to steal his work.
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