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It seems to be that the height is created by the old fronds decaying, doubleheader and twisted is simply a variation that occurs as a norm for some plants- like the trunk of a palm is the old fronds that have died.
Tree Ferns are very slow growing and are so common in Australia that IF you look at the list of forum's on this site, you will find one for the Australian gardeners who will give you the very best instructions for this type of fern.
I grow them here in UK and can tell you that I need to wrap mine up in straw ect for winter.
I can tell you that you water these plants not at the base root area but, shower the water into the centre of the fronds, and also wet the hairy trunk,
We love witnessing the fronds (leaves) uncurl, they start off looking like large hairy caterpillars and then this beautiful green long leaf uncurls to show off.
I wish you well with your Tree fern and you have very many years watching it SLOWLY grow up to be an adult.
I don't think she said there was a tree fern forum. There is an Australian forum http://davesgarden.com/community/forums/f/oz/all/ (If you look through the forum list, there's a section labeled "international gardening forums" where you will find Australia & a few others)