This function creates a new node and inserts it into the tree. The first parameter is the parent node; if it's NULL the node will be the root. The "labels" parameter is an array of strings which are shown in the tree, for each column one. pixmap_spacing is the spacing between the pixmap and the text.

The sibling parameter determines the position of the new node. If it is NULL, it will be appended to the parents childen as the last element. If the sibling is given, the new node will be inserted just before it.