Shaun Tan could never have imagined what would evolve from a series of sketches he started in his mid-twenties - "strange little whispers that the mind would normally censor" - when he was struggling to find direction as an artist.

At the time, the illustrator and author felt acutely the loneliness of his profession and ended up feeling "quite lost".

"I'm not a terribly expressive person emotionally in day-to-day life - so friends and family have commented - but it comes out in drawing and writing for some reason," Tan admits.

And so he drew - small pen doodles in cheap notebooks.

"Cheap, so they don't feel important, it's very important that art-making does not feel important," he says.

"(At first) my interest was to simply represent feelings as emotional landscapes, as an artistic exercise."

But as he progressed, "though multiple sketchbook iterations", he realised many of his own suppressed feelings of isolation and loneliness were finding expression in strange apparitions.

Floating fish, menacing cities, drifting flying machines, were "like dreams resolving on paper with paint and collage".

Over a long period of time and out of "a number of other abandoned projects", his evocative picture book The Red Tree was born.

It tells the story of a young girl moving through a series of bleak landscapes after waking up to find blackened leaves falling from her bedroom ceiling.

As she wanders around a world that is "complex, puzzling and alienating", she is overtaken by many feelings.

Just as it seems all hope is lost, the girl returns to her bedroom to find a tiny red seedling has grown to fill the room with warm light.

In the two decades since it was first published, The Red Tree's extraordinary imagery continues to resonate with people across the world.

It has become, quite unintentionally, a go-to resource documenting depression.

"It's a very intuitive book ... so many people have related to the imagery very strongly over that time, especially those suffering from depression and other mental health issues," Tan says.

"It's been widely used by psychologists and psychiatrists as a means of stimulating discussion, both with patients and with their families.

"Sometimes pictures are an easier entry point for those conversations than words."

In the year before she died, Albury schoolgirl Mary Baker wrote a compelling analysis of The Red Tree for an English assignment, for which she received full marks.

In her overview she wrote that one of the most prominent themes of the book "is the unbelievable loneliness of a mental illness such as depression".

"While the majority of the book focuses on the apparent hopelessness ... the main point is not of this despondency but of inspiration, renewal and repair, the power of hope and the fact that it is always there - somewhere - you just have to be able to see it.

"A red leaf appears on every page to symbolise hope. It is always in different positions and often hidden to confirm that you just have to look hard enough to find it.

"Every image has profound meaning."

It is heartbreakingly clear Tan's work resonated with this articulate and insightful girl, who took her life in 2011 at the age of just 15.

Mary's parents reached out to Tan in the grief-ravaged months after her death and he wrote to the family, including a sketch of the girl in The Red Tree.

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Tan recalls his first contact with the Bakers came as a request to use an image from the book as part of a memorial for Mary, which he was happy to help with.

"Annette and Stuart explained that Mary had been studying my book and passed on an insightful essay that she'd written about it," he says.

"Of course, I was struck by a great sadness, first of all wishing I could speak with Mary about her essay.

"But I was comforted and also quite overwhelmed by the fact that my humble images might have such a powerful emotional meaning for one family."

On the second anniversary of Mary's death, Annette gave everyone at dinner a copy of The Red Tree.

And in the years since, she has sent off dozens of copies in the "packages" she painstakingly puts together for speakers and supporters of the annual Albury-Wodonga Winter Solstice.

The red tree has been used as an enduring symbol of hope at the annual community event the Bakers founded in 2013 to shine a light on issues around suicide and mental illness.

Annette says the book - and the artist she now calls a friend - holds a cherished place in the family's hearts.

"It's an amazing story within this story - much like the branches of the red tree," she reflects.

This year the normally shy Tan has joined the Winter Solstice albeit in an online capacity from his "winter bunker".

Tan created a charming video, sketching his character from The Red Tree, which has been artfully woven into the Winter Solstice presentation by documentary-maker Helen Newman.

He is honoured to see his work find unexpected value.

"Every artist's wish, once a work has gone out into the world, is that it will gain some kind of currency and life for others, new interpretations and uses," Tan admits.

"I don't feel a great sense of ownership over my imagery either, I feel that once a book is done, it belongs to the reader.

"Over the years I've come to recognise that this book, in particular, has many meanings for many different people, and that it has a kind of autonomous existence having left my drawing table."

Tan, who won an Academy Award for his animated adaption of another picture book he wrote and illustrated (The Lost Thing), believes the red tree is a fitting symbol for the Winter Solstice.

"It's so open and to my knowledge has not been used to represent anything previously," he says.

"Bright, vibrant, but also fragile and transitory."

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Through his artist's gaze, Tan sees COVID-19 as an opportunity for slowing society down towards introspection.

"I think we'll be contemplating it for some time to come, and hopefully do have time for reflection before rushing back to factory settings," he says.

"In my local neighbourhood and school, I have seen a great sense of community, of people sharing and checking in on each other, and I've thought much more about my social circles, wondering how people are getting on."

But Tan acknowledges the effects of isolation on the vulnerable are concerning - as they are on the voiceless.

"Much of my creative thinking is about those people, the ones we don't see or hear so much," he says.

Tan draws inspiration from "everything" - childhood memories, dreams, books, conversations, family, life.

He seeks to keep meanings as open as possible "so that someone else has space to find their own".

Tan, who was known as the "good drawer" at his Perth school and which partly compensated for always being the shortest kid in every class, now lives in Melbourne with his wife and two children.

Painting and writing are meditation - "taking long studied moments to process things, to find connections between things ... beyond the day-to-day chatter, chaos and practical worries that preoccupy most of us."

As he doodles ideas - "most of it is dreamlike nonsense" - occasionally something appears that seems "somehow profound or resonant to real-life concerns".

Something that grows and branches out to become astonishing.

Something that helps shed light on the darkness of mental illness.

Something like a little girl and a red tree.

"I realise it's enough to just show a dark thing, that alone can be immensely consoling for those confronting it in real life," Tan reflects.

"To know that you are not alone, that your experience is not so strange actually."