addSubNode
Will add subnode in tree if there are no any node with newData
If newData is greater than SortedBinaryTreeNode.data of currently checking node, will be used SortedBinaryTreeNode.rightNode
If newData is equal to SortedBinaryTreeNode.data of currently checking node - will be returned currently checking node
If newData is less than SortedBinaryTreeNode.data of currently checking node - will be used SortedBinaryTreeNode.leftNode
This process will continue until function will not find place to put SortedBinaryTreeNode with data or SortedBinaryTreeNode with SortedBinaryTreeNode.data same as newData will be found