Node A in position 1
Node B in position 2
Node C in position 3
...
Left child of Node in position K: in position 2K
Right child of Node in position K: in position 2K + 1
So D is in position 2*2, E in 2*2+1, F in 2*3, G in 2*3+1.
Parent of Node in position I: position I div 2.
Tree with N nodes does not always occupy first N array positions: