[TreeItem] Instantiation of TreeItem's is very expensive

Hi All,

I want to display in TreeView 1-2M (may be more) items. During experiments with TreeView I found that instantiation of TreeItems is very expensive operation and take a lot of time.

Instantiate Objects: 0.12657099962234497 sec.
Instantiate ArrayLists: 0.19151298701763153 sec.
Instantiate HashMaps: 0.21388199925422668 sec.
Instantiate TreeItems: 11.619612693786621 sec.

As you can see the instantiation of 1M of TreeItems in ~60 times slowly than ArrayLists or HashMaps. Is it possible to make instantiation of TreeItems less expensive?

Here is code for reproduce this problem: https://gist.github.com/maxd/4ffc557851fab9f12e80