As with nearly all the ancient gods, parallel and sometimes conflicting myths exist regarding both the traditional stories and religious practices.

Regarding Attis's Birth:
Generally speaking Both Cybele and Nana are seen as the mother of Attis, depending on the tradition. Either way they are both regarded as virgins. Nana specifically was impregnated by a Almond or Pomegranate- A Virgin Birth.[1]

Regarding Attis's Death:
Some argue that crucifixion was not the cause of the death, but rather he was killed by a boar or he castrated himself under a tree. These are all true. The issue comes down to tradition vs religious practice and the symbolism therein.
In the "Passion of Attis" that occurred in Rome around 40ad an effigy of Attis was hung on a tree, placed in a tomb for 3 days and then on the 3rd day was shown to be resurrected.[2]

The notion of "hung of a tree" is, unannounced to those not familiar with mythological symbolism, "crucifixion". As denoted by Higgins in his Anacalypsis v1 p 499:
'It was an ancient custom to use trees as gibbets for crucifixion, or, if artificial, to call the cross a tree'

In fact, in Deuteronomy, a writer speaks of hanging criminals upon a tree, as though it was a general custom and says:
" He that is hanged (on a tree) is accursed of God."[3]

Furthermore, St. Paul, as he is often referred, seems to reference the above Deuteronomy quote in the correct context when he says:
"Christ hath redeemed us from the curse of the law, being made a curse for us; for it is written, " Cursed is every one that hangeth on a tree."[4]

Regarding the overall nature of the Attis myth and its influence on Christianity, Acharya S points out:
"Attis was popular not only in Phrygia/Galatia but also in Rome, where he... had a temple on Vatican Hill for six centuries. So similar was the Attis myth to the Christian story that the Christians were forced to resort to their specious argument that the devil had created created the Attis cult first to fool Christ's followers"[5]

[1] Frazer, James.: The Golden Bough, Touchstone, 1963. p. 403
[2] Jackson, John: Christianity before Christ, AAP, p. 67
[3] Deuteronomy Chap xxi 22, 23
[4] Galatians, 3:13.
[5] Acharya S: The Christ Conspiracy, p108

Also see:
Doane, Thomas: Bible Myths and Their Parallels in Other Religions, p. 190-191