The quantity of shares contained in a basket in relation to the quantity of other shares in that basket (the weighting) is decided by the basket creator in terms of his / her strategy.
If no weightings are assigned to the shares, each different share in the basket will default to an equal weighting. For example:
If there are 10 different shares contained in a basket and no weighting is assigned to those shares then each share will have a 10% weighting.