The tree is a daily reminder of his nature-loving wife Irene, who planted the tree almost 60 years ago. She died suddenly in September 2013.
Two weeks later Mr Penistan was diagnosed with cancer.
Around the same time, somebody poisoned the tree.
“Shortly after we moved into this home Irene decided that she wanted to plant a lemon-scented gum, but she couldn’t find one anywhere,” Mr Penistan said.
“One day she came running home after taking the dog for a walk because she had found a little sapling down by the river.”
Mrs Penistan carefully dug up the young tree and the couple planted it in their frontyard where it “took off like wildfire.”
A few years later, a savage storm ripped the fledgling tree nearly in two and Mr Penistan was ready to remove it when his wife intervened.
“I had my chainsaw and my shovel ready to start digging it out, but Irene rushed over and told me she could fix it,” he said.
“She was a horticulturalist’s daughter but even so, you wouldn’t have thought she could pull it off.
“She got a big elastic bandage and a straight piece of stick and she actually put a splint on it like you would on a broken leg.
“I was a little bit embarrassed by it to be honest but we left it and the damn thing grew and grew and grew.”
The tree enjoyed special standing with the Penistan family from that point on, and eventually grew so tall that the couple’s son Adrian would use it to navigate home from anywhere in Melville while riding his bike.
In January 2014, Mr Penistan first realised that something was wrong.
“I was working in the garden one day and my son arrived and immediately pointed out that the tree looked like it was dying,” he said.
Consulting arboriculturist Jonathan Epps soon confirmed their worst fears.
“Jonathon dug around a bit and came back and said ‘I’ve got some bad news for you, the tree is going to die.’”
Mr Epps discovered that somebody had drilled seven holes into the base of the tree before pouring a slow-acting poison into the cavities.
“It was clear that this had been a malicious act. The poison smell was incredibly strong and the tree was in real trouble,” he said.
“I haven’t inspected the tree since 2014 but the last time I did I noted that the holes had started to cover over which meant it was at least trying to recover at that point.
“Even so, with the condition it was in I would have to say I think it has a very low chance of recovery.
Mr Penistan spent more than $2000 to have the tree pruned back to remove dead and dying limbs and refused to give up hope.
“I don’t physically look at it because I get pretty upset about it,” he said.
“We’ve been together for 57 years.
“I know it’s only a one in 100 or one in 200 chance but it’s my dream that the tree will come back to life.”