It isn't referred to in any obvious terms as a "world-tree" in the mainstream mythology, but the concept might be present in the story of the wedding of Zeus and Hera, with which Zeus' favourite illegitimate son Herakles (one of Hera's most hated stepchildren) is ultimately connected. Zeus and Hera get married at the point of transition between the end of the cataclysmic Titans' War and the beginning of the state of equilibrium in which the gods are able to create humankind.
According to Apollodorus, Gaia gave Zeus some magic golden apples as a wedding present. In his Astronomica, Hyginus cites Pherecydes as his source in saying that these apples came on branches which Hera asked Gaia to plant in her gardens (which, according to Dick Caldwell, are among several paradises in this mythology) near Mt Atlas in Morocco. At the time northwestern Africa was supposed to be the western end of the world, bordering the dusky side of the Okeanos [Oceanus] River (= the eastern Atlantic Ocean).
The planted branches thus grew into a tree which Hera appointed the nymphs called the Hesperides to watch over. The nymphs were, however, untrustworthy and would pilfer the magic fruit as it grew. For this reason Hera installed a guardian to watch over both the tree and the nymphs, and this new security feature was the hundred-headed dragon Ladon. Apollodorus calls Ladon immortal but Hyginus reports that he was slain by Herakles, who had been sent by his slave-master, King Eurystheus of Argolis, to steal the apples as the eleventh of his twelve labours.
A few elements of the story might lead to the expectation that the apple-tree of the Hesperides is a gigantic organism. In ancient artwork Ladon is often depicted as coiled around the tree, a phenomenon corroborated in writing by Pausanias, in his inventory of the myth-related images he encounters while travelling through Olympia. Dragons in most mythologies, especially that of Greece, are typically colossal monsters. Hyginus and Seneca both say that Ladon is "huge", and it might be fair to expect that the creature resembles his monstrous parents Typhoeus [Typhon] and Ekhidna [Echidna] in size to at least some extent.
In the same art pieces depicting Ladon entwined upon the tree, Herakles and the Hesperides appear to be not much smaller than both the beast and the plant. The gigantic size of the Hesperides could be explained based on their parentage too, since both their parents are Titans (going by at least one interpretation of Diodorus Siculus). This still leaves Herakles unaccounted for, but it could be argued that in ancient Greek art, on account of the lack of space in the medium, portrayals of Titans, giants and monsters renders them in pretty much the same size as the gods and heroes alongside whom they are depicted.
Whatever the case may be regarding the tree's stature, its story does strongly hint that it is a cosmic structure in the sense that it links a few different parts of the universe together. Far enough into the Okeanos River away from dry land would bring one into the Underworld. Hera's Gardens, where the tree is located, are on the shores of the Okeanos, on the Evening side of the universe, where Night (Nyx), the mother of Death (Thanatos), begins, and close to which Night's husband Darkness (Erebos) dwells. Contrasting this, the Hesperides, "Daughters of Evening," serve as the guardians of immortality and deathlessness, represented by the apples. Apollodorus claims that the Atlas Mountain of this story is not in Africa but in the land of the Hyperboreans in the extreme north. This would be in the same direction of the lands of the Norsemen, whose gods are immortal because they feed on golden apples which restore their youth to them.
Atlas, the sky-pillar, who keeps Heaven (or at least a portion thereof) from coming crashing down, is strongly associated with Hera's magic tree, so much so that Ovid's Metamorphoses portrays him as the owner of the tree and its fruit. Perhaps in this account the tree acts as the Titan's proxy, bearing the responsibility of holding the sky up, and thereby being a conduit between Heaven and Earth, which conduit is also located on the border of the netherworld.
There are striking parallels, together with interesting contrasts, between this story and the drama surrounding a tree (or two trees) in a paradise garden at the beginning of the Bible. As the Wikipedia article you've quoted says, the world tree concept "may also be strongly connected to the motif of the tree of life."