Get parent node of a proto_tree

See proto_item_get_parent() in proto.h

Update: Upon doing some research: I think that the code to get the parent_proto_tree is as follows:

subtree_item = proto_tree_get_parent(subtree);  // returns (proto_item *)subtree
parent_item  = proto_item_get_parent(subtree_item);
parent_tree  = proto_item_get_subtree(parent_item);

AFAIKT there are no instances of this usage in the current Wireshark source.

What I do see in a number of dissectors is code like the following:

proto_item_append_text(proto_item_get_parent(proto_tree_get_parent(tree)), "...");

which appends text to the item "1 level up" from the item for the current tree.